Harris’ momentum is growing. Our polling expert explains whether it’ll last.

Kamala Harris stole Donald Trump’s Republican convention bounce.

Now, polling conducted in the immediate run up to this week’s Democratic convention in Chicago shows the vice president entering not just with momentum, but with a slight advantage over Trump nationally and in most key battleground states — a dramatic reversal from the big hole President Joe Biden was in before he abandoned his candidacy just four weeks ago.

Just on Sunday, a new ABC News/Washington Post/Ipsos national poll showed Harris ahead by 6 points among likely voters, 51 percent to 45 percent, while a CBS News/YouGov poll gave Harris a 3-point lead.

Harris has also seized a small lead in enough swing states to give her an Electoral College majority, a deeply worrying sign for Trump in the crucial last months of the campaign. The vice president held advantages of at least 4 points in four state polls from The New York Times and Siena College — Arizona, Michigan, Pennsylvania and Wisconsin — that alone would hand Harris enough electoral votes to win the presidency, even if she lost the other swing states.

The former president is still well within striking distance, even after struggling to regain his footing against a new opponent. According to the latest FiveThirtyEight polling averages, Trump would only need to flip one of the three “blue wall” states — Michigan, Pennsylvania or Wisconsin — in order to win in November, as long as he takes all of the states where he is currently ahead of Harris in polling averages.

But the timing of Harris’ ascendance is perhaps even more notable than its magnitude and speed. She became a candidate on July 21, just eight days after the assassination attempt against the former president and less than 72 hours after Trump’s acceptance speech at the Republican convention in Milwaukee. Republicans had rallied behind Trump after the shooting and his own convention, and he appeared to be in a much stronger position than Biden, his opponent at the time.

In a typical campaign, the summer is the most volatile time, with the party not currently holding the White House receiving a polling bump following its convention — which by tradition comes first. The president’s party then responds with a corresponding surge that usually cancels out the earlier change.

But in this case, it’s Harris who has had the wind at her back since the Republican convention concluded last month. It’s far from a sure thing that Harris will continue to rise through the end of August — though some Republicans are preparing for the possibility that Harris will have a larger lead on Labor Day than she does now — but adding a convention bump on top of that could position Harris as a significant favorite in the race.

That’s because, historically, voters’ preferences are typically all-but-solidified at the conclusion of the conventions, and any changes in polling after the conventions are typically modest. But this has been anything but the typical campaign.

Here are five takeaways from the pre-convention polling:

Trump leads on issues but trails on personality.

How is Trump trailing Harris when voters trust him more on the economy, the issue they say is most important to their vote? Because they don’t like or trust him more broadly.

In the ABC News/Washington Post/Ipsos poll, Americans said they trust Trump over Harris when it comes to dealing with the economy — which nearly nine-in-10 respondents said was very important to their vote — 46 percent to 37 percent.

But it’s clear why Harris leads after looking at the candidates’ personal attributes.

Poll respondents are split on Harris’ image: 45 percent view the vice president favorably, while 44 percent view her unfavorably. For Trump, only 35 percent have a favorable opinion of him. The majority, 57 percent, view him unfavorably.

Back in July, Trump held a 31-point lead over Biden on the question of which candidate “is in good enough physical health to serve effectively as president.” In the new poll, the 78-year-old Trump is at a 30-point deficit on the same question.

Similarly, Harris, 59, leads Trump on which candidate “is honest and trustworthy” (by 15 points), “has the mental sharpness it takes to serve effectively as president” (by 9 points), “understands the problems of people like you” (by 7 points) and “represents your personal values” (by 6 points).

The Sun Belt is up for grabs again.

The reasons for Harris’ competitiveness in the four Sun Belt swing states go beyond just the topline numbers. She’s attracting voters a Democratic candidate needs in younger, more diverse states.

In the ABC News/Washington Post/Ipsos poll, Harris leads among those under age 40, 57 percent to 37 percent, even though Biden and Trump were neck-and-neck with the under-40 set last month.

Harris is also outrunning Biden among Black (more on that below) and Hispanic voters, who make up large segments of the electorates in Arizona, Georgia, Nevada and North Carolina.

Even before the June debate, Biden’s decline was especially concentrated among young and nonwhite voters, and many of those Sun Belt states looked out of reach. A path to an Electoral College majority still existed if he ran the table in the Rust Belt, but Harris’ recovery gives her a chance to win even if Trump picks off one of those northern states.

Black voters have come back to Harris.

In the ABC News/Washington Post/Ipsos poll, Black Americans broke for Harris, 83 percent to 11 percent — far more in line with recent precedent. Same with the New York Times/Siena College Sun Belt-state polls, in which Harris led, 84 percent to 11 percent, among Black likely voters.

And Suffolk University/USA Today polling of Black voters in Michigan and Pennsylvania shows Trump pulling in only about 10 percent among Black voters, about where he was in 2020.

There are still some polls that show historically high support for Trump, as a Republican — like last week’s Fox News poll, which had the former president capturing 26 percent of Black voters. But generally speaking, the trend points to Harris, who is of both Black and South Asian ancestry, winning a more comparable share of Black voters.

Harris is winning the “democracy” argument.

Biden grounded his campaign in the argument that democracy was at stake — and threatened if Trump won the election.

Harris isn’t being as direct with her own messaging on the issue, but she’s still building an advantage over Trump. More than three-in-four Americans, 77 percent, say protecting democracy is at least very important to their vote in the ABC News/Washington Post/Ipsos poll, below only the economy and inflation and tied with health care and crime on the list of issues presented.

And Harris is more trusted on protecting democracy in the poll, 43 percent to 37 percent. Similarly, Sun Belt-state likely voters gave Harris an 8-point edge when it comes to handling democracy, 52 percent to 44 percent, in the New York Times/Siena College poll.

Yes, the convention bump actually matters.

While it’s perhaps not surprising that candidates see their poll numbers go up during their party’s convention — a made-for-TV infomercial for them and their policies — that doesn’t mean the conventions don’t matter.

To that point, Harris — who leads Trump by 1.4 percentage points in the RealClearPolitics polling average and 2.6 points in the FiveThirtyEight average — enters her convention in a significantly weaker position than Biden in 2020, but a stronger position than Hillary Clinton in 2016.

Clinton actually trailed Trump by less than a point in the RealClearPolitics average at the start of the 2016 Democratic convention because Trump was enjoying his convention bounce (the conventions were on back-to-back weeks in July 2016 because the Olympics, which were held in the Southern Hemisphere, began later in the summer than usual).

Historically, a party gets about a 4-point bounce from its convention, according to the book “The Timeline of Presidential Elections: How Campaigns Do (and Do Not) Matter.” But these bounces don’t always cancel each other out — and, most importantly, the party that sees the greatest improvement during the conventions “maintains its gain in the final week’s polls,” according to the authors, Robert S. Erikson and Christopher Wlezien.

“In other words, its poll numbers do not fade but instead stay constant post-conventions to the final week,” they write.