An unprecedented summer has turned the presidential race on its head with two months to go until Election Day, showing a dead heat in key states between Democrat Kamala Harris and Republican Donald Trump as both candidates gear up for a final blitz after the Labor Day holiday weekend.

A race that was slipping away from President Joe Biden is competitive again after he withdrew July 21 and passed the baton to his vice president, who has captured support from key groups that had soured on him, most notably young and Black voters.

Harris, 59, has turned the issue of age from a potentially fatal liability to an asset for Democrats against the 78-year-old Trump. The former president, who was running with confidence against Biden, has appeared rattled at times by Harris, launching personal and racial attacks against a rival who would be the first woman and the first Indian American to be president. She has brushed them off.

“It’s a toss-up race,” Republican strategist Brad Todd said, cautioning that the GOP’s fortunes are not as bright as they were when the Democratic nominee was the 81-year-old Biden.

Todd urged Trump to stay focused on defining Harris as a “far-left candidate” by highlighting the smorgasbord of positions she took during her 2020 campaign — on health care, energy, immigration and more. Harris has since sought to pivot to the center, while saying that her “values haven’t changed” in the last five years.

“To win, Donald Trump has to hold her accountable for the things she said she believes,” he said. “But thus far, he’s not shown a lot of interest in that.”

The summer of 2024 has delivered a sequence of events unseen in modern times, including an unusually early debate that proved fatal for Biden’s already fading re-election hopes, an assassination attempt on Trump and a GOP convention that came across as a Trump victory party. Biden turned the race on its head by dropping out, passing the buck to Harris who quickly locked up the nomination — and rapidly surged in the polls to a dead heat. The late-August Democratic convention revealed a jubilant and rejuvenated party, just before Robert F. Kennedy Jr. ended his independent bid and endorsed Trump. Harris and Trump are scheduled for their first one-on-one debate next week on Sept. 10.

‘Fundamentally a dogfight’

Despite their momentum, Democrats say the race is far from over.

“I still think it’s fundamentally a dogfight,” said Bill Burton, a political consultant who worked on Barack Obama’s 2008 campaign, praising Harris for running a “perfect” campaign so far.

Burton said it’s difficult to imagine this level of Democratic excitement if Biden were still the candidate. “She has peaked at the exact right moment,” he said. “As long as she keeps her rudder steady, I think that she’s going to do well.”

Harris leads Trump by 4 points in a USA Today/Suffolk poll and by 2 points in a Wall Street Journal survey. Recent polls of key states that Biden narrowly won in 2020 — including Michigan, Wisconsin and Pennsylvania — show a close race with a narrow Harris edge. In addition to being competitive in those “blue wall” states, Harris has put the Sun Belt states of Georgia, Arizona, Nevada and North Carolina, which were falling away from Biden, back in play.

In a memo Sunday, Harris campaign chair Jen O’Malley Dillon wrote: “[M]ake no mistake: we head into the final stretch of this race as the clear underdogs. Donald Trump has a motivated base of support, with more support and higher favorability than he has had at any point since 2020.”

Burton said Harris still has work to do in bringing home key constituencies, most notably Black voters, as Trump seeks to peel off a slice of younger Black men.

“I think some of the support with white voters” that’s showing up in the polls today “is going to be a little superficial, and she’ll have to make up for it,” Burton said.

“Watch Black voters,” he said. “That is the place where I think there’s the most opportunity and most concern.”

Both candidates are seeking to reduce their vulnerabilities by reversing their unpopular positions from the past. Harris has disavowed left-wing ideas she backed in 2019, such as Medicare for All and decriminalizing migration. Trump, while bragging about his anti-abortion record, is backtracking on his support for federal abortion restrictions and suggesting he won’t try to repeal “Obamacare” after fighting to do so as president.

Unique dynamics in the fight for Congress

The tightening presidential race has narrowed the battle for Congress, which comes with unique dynamics: The Senate majority runs through red states such as Ohio and Montana, while the race for the House goes through blue states such as California and New York.

In the closely divided House, a few-dozen battleground districts are poised to decide which party is in control. The playing field has narrowed dramatically in recent cycles because of partisan gerrymandering and regional polarization, where urban areas vote Democrat and rural areas vote Republican.

The “generic ballot” — voter preferences on which party they want to see in control of Congress — has improved slightly for Democrats since Biden dropped out, but it’s still tight. Democrats led by 1 point in a Wall Street Journal poll, by 1 point in a Reuters poll and by 2 points in an Economist poll — all within the margin of error.

The Senate map has gifted Republicans a golden opportunity to capture control, even if Democrats have a strong year. Democrats currently hold 51 seats and have conceded that they’ll lose West Virginia with the retirement of Sen. Joe Manchin. That means Republicans can clinch the majority by defeating Democrats in one of two red states where Trump is coasting to victory: Sen. Jon Tester of Montana and Sen. Sherrod Brown of Ohio.

Most public polls show Tester trailing — unlike 2018, when he led his GOP opponent and won — while Brown is narrowly ahead.

Todd, the GOP strategist, said 51 seats was “a certainty” and argued the party should aim for a bigger majority like 53 or 54 seats.

“Jon Tester is literally as dead as the Thanksgiving turkey,” he said.

A national Democrat working on Senate races disputed that view, saying: “This is a tight race that’s within the margin of error — that’s the kind of race Tester always faces and knows how to win.”

Unlike in 2022, when Republicans were talking up a red wave and a large majority that famously failed to materialize, some insiders say they’ll be content even with a narrow majority this year.

“The goal is to flip the Senate,” a GOP strategist working on Senate races said. “To that end, Tim Sheehy [in Montana] is the most important man in the country, with Bernie Moreno [in Ohio] also being in contention.”

There are five ultracompetitive states where Democrats are also defending seats: Michigan, Pennsylvania, Wisconsin, Arizona and Nevada. Polls show Democratic candidates have the advantage in all five, and Republicans admit they’re underdogs in each of them.

“The growing view among Republican strategists is that Michigan is the best pickup opportunity in the country, of the purple states,” the GOP strategist said, referring to an open seat vacated by Sen. Debbie Stabenow, D-Mich.

Democrats see glimmers of hope in Florida and Texas, two red-leaning states where GOP Sens. Rick Scott and Ted Cruz are favorites to hold on, although some surveys show their leads are narrow.

“If I were a Republican I would be very nervous about what we’re starting to see in some of the polling out of Texas and Florida,” Burton said. Colin Allred in Texas and Debbie Mucarsel Powell in Florida “are running great campaigns … They very well could be on defense [and that] could get in the way of them getting a majority,” he said.

This article was originally published on NBCNews.com