One Friday last month, Jamie Raskin, a Democratic congressman from Maryland, spent a chunk of his day in court securing a protective order.

It was not his first. Mr. Raskin, who played a leading role in Donald J. Trump’s second impeachment hearing, said he received about 50 menacing calls, emails and letters every month that are turned over to the Capitol Police.

His latest court visit was prompted by a man who showed up at his house and screamed in his face about the Covid-19 vaccine, Mr. Trump’s impeachment and gender-related surgeries. Nearly two years earlier, the same man, with his 3-year-old son in his arms, had yelled profanities at Mr. Raskin at a July 4 parade, according to a police report.

“I told the judge I don’t care about him getting jail time. He just needs some parenting lessons,” Mr. Raskin said.

Mr. Raskin was far from the only government official staring down the uglier side of public service in America in recent weeks. Since late March, bomb threats closed libraries in Durham, N.C.; Reading, Mass.; and Lancaster, Pa., and suspended operations at a courthouse in Franklin County, Pa. In Bakersfield, Calif., an activist protesting the war in Gaza was arrested after telling City Council members: “We’ll see you at your house. We’ll murder you.”

A Florida man was sentenced to 14 months in prison for leaving a voice mail message promising to “come kill” Chief Justice John Roberts.

And Mr. Trump, the presumptive Republican presidential nominee, refused to rule out violence if he were to lose in November. “It always depends on the fairness of the election,” he said in an interview late last month.

This was just a typical month in American public life, where a steady undercurrent of violence and physical risk has become a new normal. From City Hall to Congress, public officials increasingly describe threats and harassment as a routine part of their jobs. Often masked by online anonymity and propelled by extreme political views, the barrage of menace has changed how public officials do their work, terrified their families and driven some from public life altogether.

By almost all measures, the evidence of the trend is striking. Last year, more than 450 federal judges were targeted with threats, a roughly 150 percent increase from 2019, according to the United States Marshals Service. The U.S. Capitol Police investigated more than 8,000 threats to members of Congress last year, up more than 50 percent from 2018. The agency recently added three full-time prosecutors to handle the volume.

More than 80 percent of local officials said they had been threatened or harassed, according to a survey conducted in 2021 by the National League of Cities.

“People are threatening not just the prosecutor, the special counsel, the judge but also family members,” said Ronald L. Davis, director of the U.S. Marshals Service. Lisa Monaco, the deputy attorney general, said she saw “an environment where disagreement is increasingly tipping over” into “violent threats.”

It is still rare for those threats to tip into action, experts said, but such instances have increased. Some capture national attention for weeks. The mass shootings at the Tree of Life synagogue in Pittsburgh in 2018 and the Tops Friendly supermarket in Buffalo in 2022 were both carried out by perpetrators who expressed extreme right-wing views. Trump supporters’ riot at the U.S. Capitol on Jan. 6, 2021, was one of the largest acts of political violence in modern American history.

Surveys have found increasing public support for politicized violence among both Republicans and Democrats in recent years. A study released last fall by the University of California, Davis, found that nearly one in three respondents considered violence justified to advance some political objectives, including “to stop an election from being stolen.”

“Although actual acts of political violence in America are still quite low compared to some other countries, we’re now in a position where there has been enough violence that the threats are credible,” said Rachel Kleinfeld, a senior fellow at the Carnegie Endowment for International Peace who studies political violence.

Violence — and the threat of it — has been a part of American politics since the nation’s founding. But experts describe this moment as particularly volatile, thanks in great part to social media platforms that can amplify anonymous outrage, spread misinformation and conspiracy theories and turn a little-known public employee into a target.

No politician has harnessed the ferocious power of those platforms like Mr. Trump. The former president has long used personal attacks as a strategy to intimidate his adversaries. As he campaigns to return to the White House, he has turned that tactic on the judges and prosecutors involved in his various legal cases, all of whom have subsequently been threatened.

Democrats by and large have been the loudest voices in trying to quell political violence, although many on the right have accused them of insufficiently condemning unruly left-wing protesters on college campuses and at the homes of Supreme Court justices. After Senator Chuck Schumer, Democrat of New York, warned in 2020 that Supreme Court justices would “pay the price” if they eliminated federal abortion rights, Chief Justice Roberts called the statement “dangerous.”

Researchers say the climate of intimidation is thriving on political division and distrust, and feeding off other social ills — including mental illness, addiction and prejudice. Women are more commonly threatened than men, as are people of color, according to a Princeton University survey of local officials.

There is little research on the political views of those behind the onslaught of abuse. Some surveys show that Republican officeholders are more likely to report being targeted, often from members of their own party. Research does show, however, that recent acts of political violence are more likely to be carried out by perpetrators aligned with right-wing causes and beliefs.

Public officials at all levels are changing how they do their jobs in response. Many report feeling less willing to run again or seek higher office, and some are reluctant to take on controversial issues. Turnover among election workers has spiked since 2020; even librarians describe feeling vulnerable.

“These attacks are not coming from people who are looking for solutions,” said Clarence Anthony, the executive director of the National League of Cities. “They’re looking for confrontation.”

Joe Chimenti started getting death threats about a year after he took office as chairman of the board of supervisors in Shasta County, Calif., in 2019. The normally sleepy county in Northern California had been thrown into tumult by a wave of anti-government sentiment that started with the coronavirus pandemic. It grew worse after Mr. Trump falsely claimed that the 2020 election had been stolen.

Tired of violent threats and constant disruptions at meetings, Mr. Chimenti, a Republican, decided not to run for a second term. Elected in his place was a man who had repeated conspiracy theories about voting machines and who tried to hire a county executive who had called on Shasta County to secede from California.

Mr. Chimenti said he’d had enough of the abuse. “I got into this to make a difference, but I thought, Why do I want to put up with this?”

‘I Just Don’t Answer My Phone’

Fred Upton, who served as a Republican representative from Michigan for 36 years, was used to taking heat from the public. But he had never experienced anything like the backlash from his decision to vote to impeach Mr. Trump for his role in the Jan. 6 Capitol attack.

He received so many threats that he asked the local police to set up motion-activated cameras outside his home in Michigan. He installed panic buttons in his district offices and stopped notifying the public in advance of his speaking engagements. He also added a second exit door to his House office in Washington in case he or his staff needed to escape from an intruder.

After he voted in favor of President Biden’s infrastructure bill in late 2021, Representative Marjorie Taylor Greene, a fellow Republican, called him a traitor and posted his office number on her social media accounts.

“I hope you die,” one caller said in a voice mail message he received soon after. “I hope everybody in your [expletive] family dies.”

When Mr. Upton left office after his district was redrawn, he assumed the threats would stop. But he continues to receive menacing calls and letters at his home in Western Michigan.

“I just don’t answer my phone anymore, ever,” he said.

Political violence in American is not new. Left-wing activists set off bombs in the Capitol in 1983 and in 1971; five lawmakers were shot by Puerto Rican nationalists in the House chamber in 1954; a pro-German professor planted a bomb in a Senate reception room in 1915. Four presidents have been assassinated.

For decades after the Civil War, it was common for white Southerners to threaten Republican lawmakers, said Kate Masur, a professor of history at Northwestern University. “It’s hard for us to imagine how violent the United States was in the 19th century.”

But researchers view the internet as a new accelerant. Nearly three-quarters of all threats are not made in person, according to a recent Princeton analysis, making it difficult for law enforcement to identify the source.

Technology has facilitated other forms of often-anonymous harassment as well. “Swatting” — making hoax 911 calls designed to set off a police response to a target’s home — has become more common, with a spate of recent incidents involving lawmakers, mayors, judges and the special counsel investigating Mr. Trump. In January, Jay Ashcroft, the Republican secretary of state in Missouri, was ordered from his house at gunpoint by armed officers responding to a bogus call that there had been a shooting at his home. No one has been charged in the event.

“Doxxing,” or publishing personal information online — thus giving people an opportunity to harass or threaten — has been used against a wide range of public officials and even jurors in the Trump cases.

For federal lawmakers, the prospect of physical harm has long been part of the job — one that was painfully illustrated by the shooting in 2011 that gravely wounded Gabby Giffords, then an Arizona congresswoman, and by the assault on the Republican congressional baseball team in 2017 by a gunman upset by Mr. Trump’s election. On Friday, the man who had broken into the home of Nancy Pelosi, the former House speaker, and bludgeoned her husband with a hammer was sentenced to 30 years in prison.

Many public officials say they have become accustomed to managing their fears and insist they are not affected. But there is evidence that the threats and intimidation can influence decisions.

Senator Mitt Romney, a Republican from Utah who is retiring at the end of this year, told a biographer that some G.O.P. lawmakers voted not to impeach and convict Mr. Trump after the Jan. 6 attack because they were afraid for their safety if they crossed his supporters. Mr. Romney did not identify the legislators by name and declined an interview for this article.

Andrew Hitt, the former head of the Republican Party in Wisconsin, agreed to go along with the Trump campaign’s failed scheme to overturn the 2020 election because he was “scared to death,” he told “60 Minutes.”

“It was not a safe time,” he said.

‘Who Is the WORST?’

Four days after Mr. Trump was indicted in August in a federal election interference case, the presiding judge, Tanya S. Chutkan, received an alarming voice mail message at her chambers.

“If Trump doesn’t get elected in 2024, we are coming to kill you,” the caller said, according to court documents.

Investigators tracked the message to Abigail Jo Shry, a 43-year-old Texas woman who was already facing state charges related to similar threats against two Texas state senators, a Democrat and a Republican.

Ms. Shry has a history of drug and alcohol abuse and “gets all her information from the internet,” her father testified. “You can get anything you want to off the internet. And, you know, it will work you up.” (Ms. Shry’s lawyer declined to comment.)

Mr. Trump has been relentless in attacking the judges overseeing the criminal and civil cases that have confronted him of late. Last month, he asked, “Who is the WORST, most EVIL and most CORRUPT JUDGE?” in a social media post that named the judges.

They are being inundated. At least three of them, including Judge Chutkan, have been swatted. In February, a woman was sentenced to three years in prison for threatening Judge Aileen Cannon, who is overseeing the federal criminal case against Mr. Trump involving mishandling classified documents.

Last month, a resident of Lancaster, N.Y., pleaded guilty to making death threats against Judge Arthur F. Engoron, who presided over a civil fraud trial against Mr. Trump in Manhattan this year, as well as threats against Letitia James, the New York attorney general, who brought the case.

The judges have been clear that Mr. Trump’s posts make an impact. “When defendant has publicly attacked individuals, including on matters related to this case, those individuals are consequently threatened and harassed,” Judge Chutkan wrote in a gag order trying to limit Mr. Trump’s public remarks.

The prospect of being a target for abuse has already deterred some from participating in cases involving Mr. Trump. During a February court hearing in Atlanta, former Gov. Roy Barnes of Georgia, a Democrat, said that Fani T. Willis, the district attorney of Fulton County, had asked him to lead the prosecution of Mr. Trump for election interference in Georgia.

Mr. Barnes declined, explaining: “I wasn’t going to live with bodyguards for the rest of my life.”

Ms. Willis has left her home amid threats, and the county pays about $4,000 a month for her new housing. Her staff was outfitted with bulletproof vests. This month, a Californian was indicted after threatening in the comment section of a YouTube video to kill her “like a dog.”

Intimidation Close to Home

Local officials are feeling the pressure.

Election officials — from secretaries of state to poll workers — have faced hostility and abuse after Mr. Trump’s false claims of fraud in the 2020 election, leading to resignations and difficulty recruiting and retaining staff members and volunteers. Such threats “endanger our democracy itself,” Attorney General Merrick Garland said this week.

Local libraries have also become targets amid a heated campaign to ban books and cancel events aimed at members of the L.G.B.T.Q. community. Bomb threats were reported by 32 of the American Library Association’s member institutions last year, compared with two the year before and none in 2021.

Carolyn Foote, a retired librarian in Austin, Texas, who co-founded a group that supports librarians, said her members had become used to being called “pedophile, groomer, pornographer.”

Proving that ugly and hostile language has crossed the line from First Amendment-protected speech to credible threat can be difficult. Experts say prosecutions became even harder last year after the Supreme Court raised the bar for what qualifies as a credible threat, ruling that the person making the threat has to “have some subjective understanding of the threatening nature of his statements.”

In Bakersfield, Calif., a lawyer for Riddhi Patel, the activist who spoke of murdering City Council members after urging them to take up a Gaza cease-fire resolution, said her statement was not a crime. She has pleaded not guilty to 21 felony charges.

“It’s clear that this was not a true criminal threat, which under California law must be, among other things, credible, specific, immediate and unconditional,” said Peter Kang, the public defender of Kern County, which includes Bakersfield. “Instead, what we hear are Ms. Patel’s strong, passionate expressions, which fall within the bounds of constitutionally protected speech.”

Local officials say they have become accustomed to dealing with vitriol and anger that they can do little about. In Nevada County, Calif., Natalie Adona, the county clerk and recorder, said employees received a barrage of threats in 2020 from people who did not accept the election results, and again in 2022 over a mask mandate.

Ms. Adona said the county secured a restraining order against one of three people who forced their way into the building. But her staff has had to learn to endure and defuse confrontations.

“A lot of what we have experienced falls into this gray area,” Ms. Adona said. “It makes you look over your shoulder.”

Kitty Bennett contributed research