Kamala Harris leads Donald Trump in our nationwide poll tracker

THERE ARE no “quick fixes” in election campaigns. Kamala Harris’s entry into the presidential election puts this conventional wisdom to the test. In two weeks as the Democratic Party’s presumptive nominee, the vice-president has broken fundraising records and enthused the Democratic base. Her rise to the nomination has been smooth, although Republican attacks on her have barely begun. Now, with enough polling to see the effect of her candidacy, The Economist has published an updated poll tracker. It shows Ms Harris leading her opponent, Donald Trump, by 47% to 45% in the national popular vote. This is the first lead for the likely Democratic candidate since October 2023.

Along with the new candidate, our tracker has an updated methodology, designed to account for the rapidly shifting race. Support for each candidate changes each day. Each poll is an imperfect estimate of the state of play. We use a Bayesian statistical model to simulate the most likely “true” support for a candidate on each day, taking into account differences in methodology and the partisan tilt of individual polling firms. To reflect election-day dynamics and the importance of turnout in American elections, our tracker puts greater weight on head-to-head polls (which exclude third-party candidates) and those that survey “likely voters” (rather than all registered voters or all adults).

Our tracker relies on polls that included Mr Trump and Joe Biden up until July 21st, when Mr Biden withdrew from the election, then switches to polls that take in Ms Harris. It does not use “hypothetical” polling from before she became the candidate, which can be misleading. Instead, the tracker jumps on July 21st to reflect the new election campaign, but retains useful information about polls from before that date. Polls, after all, do not fall out of a coconut tree.

With all these factors accounted for, we can see how Ms Harris has changed the race. On her first day as a candidate, with the endorsement of Mr Biden, she was tied with Mr Trump on 46%. Since then she has increased her support by a point. This is a substantial improvement over the showing of Mr Biden, who trailed by around three points when he ended his presidential campaign.

Winning the nationwide popular vote may not be enough to win the presidency, though—as Hillary Clinton and Al Gore, former Democratic candidates, can attest. To secure the 270 electoral-college votes needed to win, Ms Harris must win battleground states, such as Pennsylvania and Michigan, which have leaned to the right of the country in recent elections. In 2020, Mr Biden won the popular vote by 4.5 percentage points nationwide, while eking out a win in Wisconsin—which gave him his 270th electoral vote—by only 0.6 percentage points. If Ms Harris faced the same swing-state disadvantage compared with the national vote, a three-point lead nationwide would win her only 247 electoral votes, and would return Mr Trump to the White House.

Polls also come with plenty of uncertainty, especially with three months to go before the election. Most political scientists agree that voters pay little attention to election campaigns until the final stages of the race. Until then, polling will tend to respond to the ebbs and flows of media coverage, before converging on the eventual result as the election approaches. Our presidential-election model, which will be updated shortly to reflect Ms Harris’s candidacy, accounts for this variation to forecast the final result. Our poll tracker is simply our best guess of where Americans stand today. And it shows that Mr Biden’s decision to drop out of the contest has put the election on a knife-edge. ■

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