As Democrats gathered in Chicago on Monday, eager to project an image of a liberal movement fully united behind Vice President Kamala Harris, thousands of people marched a few blocks away, presenting a thorny counterpoint.
For hours, protesters furious over the Biden administration’s support for Israel and its failure to end the war in Gaza held signs, chanted and pushed for Ms. Harris to break with the president on those issues. The loudest challenge to the opening day of the Democratic National Convention was coming not from Republicans, but from the progressive left.
“It is no longer good enough just to stand against Trump,” said Ellie Feyans-McCool, who traveled from Minnesota to attend the march, and had not yet decided whether she would support Ms. Harris or some other candidate. “You have to do good.”
From the moment Chicago was announced as host to the convention, residents and pundits alike raised concerns about the prospect of protests amid memories of violent clashes between police officers and demonstrators in the city at the Democrats’ 1968 convention. The war in Gaza, and federal lawsuits from activists accusing Chicago of infringing on their right to protest, only heightened the worries.
The protest on Monday, one of several demonstrations expected this week, was not as big as organizers had predicted. There were some clashes between activists and police officers, but nothing on the scale of 1968.
The march drew a mix of people of different ages, some in button-down shirts and others in protective gear and face masks. Some were locals, while others had traveled in on charter bus or plane. People chanted and waved signs as officers looked on. At least a dozen of the demonstrators pushed strollers as they marched.
It included a coalition of more than 200 activist groups focused on a range of progressive causes, including environmental issues, abortion rights and L.G.B.T.Q. rights, but united in anger over the war in Gaza.
Farzeen Harunani, a pro-Palestinian activist from the Chicago area, was among many in the crowd who described a feeling of political homelessness because of the Biden administration’s approach to the war.
“I’ve been blue ticket my whole life,” Ms. Harunani said. “I volunteered for the Democrats, I donated to the Democrats, door-knocked for them, phone-banked for them.”
But she said the top two candidates vying for president had left voters with a terrible choice. She said she was inclined to vote for Jill Stein, the Green Party candidate.
“All of us are very frustrated because we have a two-party system that is so ingrained,” Ms. Harunani said. “What if, rather than voting for harm or harm reduction, we could vote for no harm?”
For many in the crowd, replacing President Biden with Ms. Harris atop the Democratic ticket had no real effect on their feelings about the election.
“It’s all the same,” said Ashley Taylor-Gougé, a member of the Minnesota Anti-War Committee, who said that the group had organized two buses to bring people on the six-and-a-half-hour drive from Minneapolis to Chicago. “There have been no changes made, there have been no statements made that are in line with what we want to see happen.”
Late in the afternoon, after hours of spirited but peaceful demonstration, a number of protesters appeared to break off from the main march and move past one of the gates around the security zone near the United Center, the main convention hall. Dozens of Chicago police officers wearing helmets and carrying batons moved in on the group, urging protesters and then reporters, to leave the area. Several protesters lobbed signs and cans at the police. At least six people were detained.
In a statement, a joint information center operated by local and federal agencies said that protesters had “breached a portion of anti-scale fencing” near the United Center. The group added that law enforcement officials responded immediately and that “at no point was the inner perimeter breached.”
Earlier in the day, when a group of about a dozen people with Israeli flags marched around the park where activists had gathered, a small contingent of pro-Palestinian protesters broke off and jeered at them. Police officers worked to keep the two groups separated.
The march on Monday, which was expected to be one of the larger protests of the convention, was an early test of Chicago’s preparations. City officials, frustrated by comparisons to the 1968 convention, have sought to convey a sense of calm and confidence.
Mayor Brandon Johnson, a first-term Democrat who spoke at the convention on Monday night, has insisted that the city is ready to a host a safe convention where protesters can gather peacefully but violence will not be tolerated.
On Sunday evening, hundreds of demonstrators marched along Michigan Avenue downtown, calling for the protection of abortion and L.G.B.T.Q. rights, and peace in Gaza.
“Our officers responded exactly the way we trained them to respect First Amendment activity,” the police superintendent, Larry Snelling, said of Sunday’s protest.
One 23-year-old woman was arrested nearby on Sunday and charged with defacement of property and obstructing a police officer, he said. The woman was not part of a march, he said.
The crowd on Monday appeared to number in the low thousands, and while sizable it was smaller than organizers had expected. In an interview before the march started, an organizer said he hoped that more protesters would converge on Chicago during the week.
Unlike at the Republican National Convention in Milwaukee last month, where protests were mostly contained to the first day, activists from different groups have announced plans to gather repeatedly in Chicago.
Another protest group, focused on issues affecting poor and homeless people, marched up to the edge of the security perimeter on Monday evening. More demonstrations were scheduled on Tuesday, on Wednesday and again on Thursday evening, when Ms. Harris was expected to speak from the main stage.
Julie Bosman contributed reporting from Chicago.