Kamala Harris has wrapped up an extraordinary month.

In that short time, she’s completely transformed the 2024 presidential election. She leads in most national and battleground state polls, and the real-world signs of the enthusiasm for her candidacy are everywhere, from filled-up stadiums to record-setting campaign contributions.

All this was hard to imagine before President Biden dropped out, when a majority of Americans had an unfavorable view of her. Her previous run for president did not go well. If anything, her record in national politics saddled her with considerable baggage, including a high-profile role on immigration policy in the Biden administration and a series of unpopular policy pronouncements in her last presidential campaign.

But Vice President Harris turned around her fortunes anyway — and quickly. Clearly, many Americans did not have a strong view of her, and after a month of well-delivered speeches and upbeat appearances in the national spotlight, she has successfully reintroduced herself to the country. Now, more battleground state voters say they have a favorable than unfavorable view of her — no small feat in a jaded and divided country.

But this extraordinary turnaround wasn’t just about Ms. Harris. It was also about voters’ immense dissatisfaction with a Biden-Trump rematch, which had brought anxiety and dismay to millions. In an instant, Ms. Harris’s candidacy offered these voters what they had been yearning for: something new, different and more hopeful than that dreaded rematch. It uncorked years of pent-up Democratic enthusiasm. It let Ms. Harris bring the joy back.

As a result, she has become a certain kind of change candidate. No, she doesn’t represent a change in policy or party, but she represents the promise of a new beginning. She has also turned Donald J. Trump into a something like a candidate of the status quo, or even the past — not the policy status quo, but the candidate of a contentious and exhausting decade of American political life.

It was enough to give Ms. Harris a lead heading into her convention. If history is any indication, her edge could expand further in the next wave of polls, taken after tens of millions watched her nationally televised address.

Whether that lead will last until November will depend, in part, on the answers to these questions:

Is this just a bounce?

Ms. Harris has made a good impression, but has she made a lasting impression?

If there’s a risk in her current numbers, it’s that she’s riding a polling “bounce” — a political sugar high, fueled by positive but unsustainable event-driven media coverage.

These polling bounces are common in the wake of debates or conventions, and Ms. Harris’s last month has some of those characteristics. She benefited from multiple events that let her bask in the national spotlight: her entry into the race; the Democratic embrace of her candidacy; her vice-presidential selection. Then came the Democratic convention, a textbook case for a media-fueled surge.

As the name implies, bounces don’t usually last. But sometimes, bounces permanently reshape the race — they become bumps, if you prefer. The 1992 presidential election, for instance, was permanently changed by the Democratic convention, when an unpopular but still ill-defined Bill Clinton unified a divided party and helped drive Ross Perot out of the race (he returned to the race in the fall).

If Ms. Harris’s position mostly holds after the spotlight fades, the next question is whether her support will be resilient enough to withstand the difficulties ahead. So far, she hasn’t faced any real adversity in the campaign — there haven’t been any glaring missteps, tough news cycles or hard-hitting investigative stories. At some point, expect this to change; it typically does.

Here’s what we know: Views of Ms. Harris aren’t set in stone. A CBS News poll before the convention found just 64 percent of registered voters said they knew what she stood for. That’s what presented the opportunity for her to redefine herself over the last month. It also means it’s not safe to assume her position is durable today.

Can Trump redefine Harris?

Ms. Harris didn’t just improve her standing over the last month; Mr. Trump and the Republicans failed to define her in a negative light.

Here’s a bit of what the Republicans and Mr. Trump have tried:

None of these have seemed to land so far. Why not? It’s worth breaking them down into a few categories.

Personal attacks. For the most part, they’ve fallen flat. There’s one obvious reason: These attacks don’t really strike at her integrity.

There is no scandal or allegation that she’s part of the swamp. To be blunt: There isn’t really a reason to dislike her as a person on this list, leaving aside what you may think of her politics.

The perception of a clean record is a big deal in today’s cynical era. It’s an especially big deal against Mr. Trump, who feeds off the sense of a broken, corrupt system that looks out for elites, not the public interest. If there was one missed opportunity at the recent convention, it may have been that Ms. Harris didn’t lean into this further, by promising to take on corruption, corporate power and special interests in Washington.

Issue-based attacks. These have gotten more traction, but not much. In the last New York Times/Siena College polls, less than half of battleground state voters said Ms. Harris was “too liberal or progressive,” even though she ran a left-leaning presidential campaign five years ago.

One reason “Comrade Kamala” hasn’t landed: Ms. Harris is not a hero of the activist left, like Elizabeth Warren or Bernie Sanders. She did embrace many progressive positions in 2019, but she did so to earn the support of the left — not because she’s its natural champion. Indeed, her campaign was criticized for not clearly standing for much of anything.

Attacks on her consistency. The public may not see her as Comrade Harris, but it does see the case for “Kama-kameleon.” A majority of voters in the last Times/Siena polls agreed that she flip-flops on the most important issues.

There’s vulnerability here, but “flip-flopper” isn’t usually the most potent attack. It takes a special set of circumstances for “flip-flopper” to derail a candidacy, like flip-flopping in a way that undermines the credibility of a candidate’s central message.

John Kerry and Mitt Romney, for instance, were trying to campaign against the very positions — the Iraq War and Obamacare — that their opponents argued they had previously supported. If Ms. Harris were campaigning against Medicare for all, her previous support for the policy would be a major issue, but that’s not the case here.

Republicans seem to know this, and they’ve taken a different approach, asserting that her 2019 views on fracking, immigration and other topics represent her “real” views on the issues.

Attacks on her race and gender. After initially calling Ms. Harris a D.E.I. hire and questioning her racial identity, Mr. Trump has mostly moved on from identity-based attacks. And interestingly, she’s rarely been attacked in a way that seems focused on her gender. The jab at her laugh is one exception, but not one that resonated. Not even her critics say she’s “shrill” or “unlikable,” as some previous female candidates for president have been called.

Why haven’t these kinds of attacks landed? That’s probably worth an article in its own right, and there are a lot of possible explanations — including sexist ones, like Ms. Harris’s smile and “joyful” campaign fitting societal expectations for women. Whatever the explanation, these attacks aren’t central to the Trump campaign, at least for now.

Attacks for not actually representing change. Over the last few days, there’s been a new line of attack: She’s just more of the same failed Biden-Harris administration policies.

There’s no funny nickname or New York Post headline to go along with this attack so far, but its importance is obvious. Unlike the others, it goes to the heart of her early strength in the campaign: the notion that she represents change.

In the last Times/Siena battleground polls, half of voters said she would bring “the right kind of change” for the country, slightly more than said the same for Mr. Trump. Whether Ms. Harris’s strength rests on firm ground depends in part on why, exactly, voters were so dissatisfied with Mr. Biden and the state of the country. It’s been a central question all cycle, and even without Mr. Biden at the top of the ticket, it still has the potential to decide the election.