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ATLANTA — President Biden’s decision to drop out of the presidential race may have reset the states considered up for grabs in November, as both major-party campaigns shift their attention to the Sun Belt once again.

The seven states decided by narrow margins in 2020 — Arizona, Georgia, Michigan, Nevada, North Carolina, Pennsylvania and Wisconsin — are the primary focus of Vice President Harris and former President Donald Trump with fewer than 100 days until Election Day — and with early voting set to begin in many places weeks before that.

Four years ago, Biden narrowly won all of those states except North Carolina by stitching together a diverse coalition of voters that also gave the campaign multiple pathways to win.

But following his disastrous debate performance a month ago, polling averages showed him losing to Trump nationwide, and trailing outside the margin of error in every battleground state except the so-called “Blue Wall” states of Michigan, Pennsylvania and Wisconsin.

Now, with Harris replacing Biden as the likely Democratic nominee, early surveys of the new presidential race show a changing contest that is close, driven by a surge in Democratic enthusiasm and Harris winning back younger, nonwhite voters that had soured on Biden.

Those shifting coalitions point to improved chances for Democrats in the more diverse Sun Belt swing states of Arizona, Georgia, North Carolina and Nevada — and put the original battleground map back into place.

The latest NPR/PBS News/Marist national poll shows a statistical tie between Harris and Trump, both head to head and in a larger contest that includes minor party and independent candidates. Several state-level polls in swing states since Harris announced her candidacy show a tighter race as well.

The candidates themselves have both implicitly and explicitly acknowledged the altered political map. On the airwaves, both campaigns are launching multimillion-dollar ad buys in the key battleground states. Harris’ campaign is running a spot that highlights her background as a prosecutor and Trump’s video attacks Harris as weak on immigration issues.

Harris held a rally in Atlanta Tuesday night, the largest of the campaign so far, in front of thousands of supporters at Georgia State University’s Convocation Center.

“Georgia, it is so good to be back, and I am very clear: The path to the White House runs right through this state,” Harris said to a filled 10,000-person arena. “And you all helped us win in 2020 — and we’re gonna do it again in 2024!”

Trump and his vice presidential nominee, Ohio U.S. Sen. JD Vance, will hold a rally at the same location on Saturday.

Georgia in particular is seen as an opportunity for the Harris campaign to improve before Election Day.

Nearly a third of the electorate is Black, Atlanta’s suburbs are home to a sizable share of moderate voters who have voted for Republicans and Democrats in past elections, and the Harris campaign says it is making record staffing investments.

“In Georgia, we’re running the largest in-state operation of any Democratic presidential campaign cycle ever,” Harris campaign communications director Michael Tyler said to reporters. “Since the vice president began her candidacy, we’ve seen tremendous energy on the ground.”

The Trump campaign is not ceding focus on the Sun Belt, though.

Vance is campaigning in Nevada and Arizona this week, with a planned appearance at the U.S. southern border on Thursday.

Arizona and Georgia are also two primary states where Republicans’ “Trump Force 47” campaign strategy to use volunteers to lead targeted get-out-the-vote efforts is in full swing.

As both Trump and Harris continue to make their case to voters in these swing states over the next three months, there are still several key events that could continue to shape the contour of the race, like Harris naming her vice presidential pick, the Democratic National Convention next month in Chicago and any potential debates between Trump and Harris before voting begins.

Harris is set to announce her running mate within days, and the campaign says they will do a series of rallies, a tour that will begin on Tuesday and take them to Philadelphia, western Wisconsin, Detroit, Raleigh, N.C., Savannah, Ga., Phoenix and Las Vegas.

NPR’s Deepa Shivaram contributed reporting.