ATLANTA — Vice President Kamala Harris told a cheering, boisterous, packed arena on Tuesday that the next few months would be a serious fight and acknowledged the Democrats were right now the underdogs — but assured the crowd they would win in November.

“We have a fight in front of us,” the likely nominee said. “The momentum in this race is shifting. And there are signs Donald Trump is feeling it.”

Little more than a week ago, Georgia appeared to be slipping out of the Democrats’ reach: President Joe Biden’s campaign pledged to concentrate more on holding the Midwestern “blue wall” states and indicated they might be willing to forsake “Sun Belt” battlegrounds.

But now that Biden has bowed out of the race and Harris is the likely nominee, Democrats are expressing new hopes of an expanded electoral map and welcoming the vice president to the state that delivered Biden his narrowest victory margin in 2020 with a show of political force intended to signal a new landscape against Trump.

Harris said when she was reelected she was going to work to sign important legislation on immigration and “show Donald Trump what real leadership looks like.”

The roughly 8,000-capacity basketball arena at Georgia State University was filled to its rafters with thousands of voters waving signs, dancing to the Harris campaign soundtrack and celebrating an atmosphere that would not have been possible just 10 days ago, with the party reeling over whether the 81-year-old Biden would remain in the race after a dismal performance magnified concerns about his age and abilities.

“This is like Barack Obama 2008 on steroids for me,” said Mildred Hobson Doss, a 59-year-old who came downtown from suburban Lilburn. “I would have voted for President Biden again. But we are ready.”

Harris is hoping the rally, which featured a performance by hip-hop star Megan Thee Stallion, will help affirm her campaign’s momentum. The campaign argues that Harris' appeal to young people, working-age women and non-white voters has scrambled the dynamics in Georgia and other states that are demographically similar, from North Carolina to Nevada and Arizona.

“The energy is infectious,” said Georgia Democratic Chairwoman Nikema Williams, a congresswoman from Atlanta. “My phone has been blowing up. People want to be part of this movement.”

In a strategy memo released after the president left the race, Harris campaign chair Jen O’Malley Dillon, who held the same role for Biden, reaffirmed the importance of winning Michigan, Wisconsin and Pennsylvania, a trio of industrial states that have formed the traditional Democratic blue wall.

But she also argued that the vice president's place atop the ticket “opens up additional persuadable voters” and described them as “disproportionately Black, Latino and under 30” in places like Georgia.

“This campaign is about freedom,” said Georgia Sen. Raphael Warnock, who was there with his fellow Democratic Sen. Jon Ossoff. “So the question is, do you want to be free? Or do you want to go back?”

“When you show up, we win.”

Republicans, who still control Georgia’s state government, counter that Biden’s lagging popularity and concern over higher consumer prices and immigration will transfer to Harris in the historically conservative state.

But they concede that the landscape suddenly looks much closer to 2020 — when Biden won by about 0.25 percentage points — than when Trump was riding high after the Republican National Convention and surviving an assassination attempt.

“Trump was going to win Georgia. It was over,” said Republican consultant Brian Robinson. “The Democrats have a chance here for a reset.”

And Trump is not taking chances. Earlier Tuesday, the former president announced that he would come to Atlanta on Saturday for a rally in the same Georgia State arena.

Robinson said Harris still has plenty of liabilities, including the progressive positions she took in her failed 2020 primary campaign and her various rhetorical stumbles. But he said Harris so far in this campaign has been “in command,” and if that continues, “we have a new ballgame and she will be competitive in Georgia.”

Trump campaign spokesperson Karoline Leavitt dismissed Harris as “just as weak, failed and incompetent as Joe Biden” and said the vice president would have to explain her support of Biden administration policies that “hurt working families in Georgia over the past four years.”

The Harris campaign and Georgia Democratic officials have 24 offices across the state, including two added last weekend in metro Atlanta. Trump and the Republican National Committee opened their first Georgia offices only recently.

Democrats are betting that a combination of high turnout among traditional, core Democratic constituencies, as well as a strong showing in the suburbs and small pickups elsewhere, can be enough for Harris to carry Georgia.

Georgia Gov. Brian Kemp, a Republican, said in a recent interview that the best GOP campaigns can win comfortably in Georgia but bad efforts — combined with strong Democratic campaigns — lose. Kemp, for example, won reelection by 7.5 percentage points in 2022 over national Democratic star Stacey Abrams. Yet in the same election cycle, Georgians reelected Democratic Sen. Raphael Warnock over his Republican challenger Herschel Walker, who was endorsed by Trump.

In recent elections, Democrats have held wide advantages in the core of metro Atlanta, where Jayapal spoke. The party also performed well in Columbus and Savannah, as well as some rural, majority-Black counties. But Republicans dominated in other rural areas and small towns and cities —- where Trump has held multiple rallies in recent years.

The fast-growing, diversifying Atlanta suburbs and exurbs offer the most opportunity for swings, especially from GOP-leaning moderates disenchanted with Trump.

For Harris, that means depending on voters as varied as Michael Sleister, a white suburbanite, and Allen Smith, a Black man who lives not far from downtown Atlanta.

Sleister, who considers himself an independent, has lived in Forsyth County for 35 years. “I've voted Republican many times in my life,” he said, but not since the GOP took a rightward turn during President Barack Obama's administration.

“Now I see the Republican Party as representing a direct threat to my grandchildren,” he said, adding that he sees Trump “as just a horrible person.”

Smith is a 41-year-old Atlanta native who has become a first-time campaign volunteer since Harris became the likely nominee.

“I was driving when I heard the news about President Biden endorsing her, and I started pounding my fist — I decided right then I would do whatever I could to help her get elected,” Smith said.