By Eric Bradner, CNN

(CNN) -- Joe Biden's campaign dispatched former President Barack Obama to Atlanta on Monday in a bid to finish Democrats' four-year project of turning Georgia blue.

The state is one of three in the Southeast -- along with Florida and North Carolina -- that are all crucial for President Donald Trump to win to keep open his path to 270 electoral votes.

But its diversifying electorate, suburban swings in Democrats' favor and a series of close calls there during Trump's presidency have turned Georgia into a battleground. And the presence of two Senate seats on the ballot have made it marquee in the race for control of Congress, as well.

Georgia, along with the other Sun Belt states, is likely to be among the fastest battlegrounds to report its results on election night. That reality makes the three states indicators of whether Biden is on course for a decisive win, or if the candidates are facing a much closer race that will be largely decided by Northern battlegrounds.

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Biden isn't visiting Georgia himself in the final days of the race. But his campaign has dispatched its top surrogates to the state, including Obama's visit to Atlanta, where he campaigned with Democratic Senate candidates.

Obama told the crowd he hadn't originally planned to come to the state, but he said he was told Georgia "could be the place where we put this country back on track."

He hammered Trump for suggesting Sunday night that he might fire Dr. Anthony Fauci, the nation's leading infectious diseases expert, after the election.

"One of the few people in this administration who's been taking this seriously all along, and what'd he say? His second term plan is to fire that guy," Obama said. "I mean, they've already said they're not going to contain the pandemic. Now they want to fire the one person who could actually help them contain the pandemic."

Obama's visit followed Biden's running mate, California Sen. Kamala Harris, visiting in Georgia on Sunday.

Harris campaigned alongside Stacey Abrams, the former gubernatorial nominee who has been at the center of Democrats' effort to expand the party's electorate there.

"All that we are looking to now in terms of Georgia and the prospect of what we might accomplish in this state, in large part, we have to say thank you Stacey Abrams for the work you have done," Harris said.

She sought to motivate Democratic voters there by pointing to the late Rep. John Lewis, the civil rights icon who died this year, saying voters must "honor their ancestors" as she lambasted Trump's long history of racist comments and actions.

"It's not like it's a one-off. Don't forget when he was running for office and thinking about his political career, he had the gall to question the legitimacy of America's first Black president," Harris said of Trump, referring to his racist birther attacks on Obama.

Trump, meanwhile, visited Rome, Georgia, on Sunday night, delivering his stump speech and making clear he expects to win the state for a second time Tuesday. His presence in the state just days before the election underscored Republican concerns that Democrats could flip the state.

"I shouldn't even be here. They say I have Georgia made," Trump said.

Four years ago, Trump defeated Hillary Clinton by 5 percentage points in Georgia, a result that showed a state Republicans have dominated for more than two decades was becoming competitive.

But since then, Georgia has proved an elusive target for Democrats. In a 2017 special election for a House seat in the Atlanta suburbs, first-time candidate Jon Ossoff shattered fundraising records with a nearly $30 million haul -- a harbinger for the massive totals Democrats would raise over the next four years -- but fell short against Republican Karen Handel.

Handel then lost the seat to Democrat Lucy McBath in the 2018 midterm elections. But Democrats lost the biggest price: the governor's office, with former state House Democratic leader Abrams, who was seen as a generational rising star in the state's party, losing to Republican Brian Kemp in a close race, amid complaints that Kemp had mismanaged the state's election system in his post as secretary of state.

It was a frustrating blow and the latest in a long series of losses for Georgia Democrats. The party hasn't won major statewide races in Georgia in two decades: Bill Clinton was the party's last presidential candidate to carry the state in 1992; Democrats last won a governor's race in 1998 and a Senate race there in 2000, in a special election.

Still, its rapidly diversifying population and the suburban shift in Democrats' favor nationwide has made Georgia an attractive target.

Nikema Williams, the chairwoman of the Democratic Party of Georgia, said the state's evolution from 2016 -- with a network of female activists engaging starting in the 2017 House special election, through Abrams' party-building in 2018, and protests over racial injustice in 2020 -- has built the moment party loyalists there have been waiting for.

"It's that perfect opportunity where people are still active and engaged, and the women who were activated after the 2016 election never left the party; never left their activism, and have continued to build at this date. ... Everything coming together in this pivotal moment," Williams said. "Georgia is ready to flip right now, because of all of the work that has happened."

In addition to Georgia's 16 electoral votes at stake in the presidential race, Democrats are closely watching two Senate races in Georgia: Ossoff's challenge to Republican Sen. David Perdue, and a special election in which Democratic Rev. Raphael Warnock faces several opponents, including incumbent Republican Sen. Kelly Loeffler. If no candidate crosses the 50% threshold, one or both Senate races could then move to a runoff election featuring the top two finishers.

Obama also criticized Perdue and Loeffler, the two Republican incumbent senators.

"Your two senators publicly were telling you that the virus would be no big deal. But behind closed doors, they were making a bunch of moves in the stock market to try to make sure their portfolios were protected instead of making sure you were protected. Man, that's shady," Obama said.

Obama called Loeffler and Perdue "the dynamic duo of doing wrong" and said "Georgia was definitely not on their mind."

If election night goes perfectly for Georgia Democrats, they also have a shot at flipping enough seats to take control of the state House of Representatives. Such a win could pay dividends on the national and state levels for a decade, because it would give Democrats a seat at the table when the legislature redraws congressional and state legislative district lines next year during the once-a-decade redistricting process.

Democrats have also turned Georgia into a costly state for the GOP to defend: Biden and the Democratic National Committee have spent more than $10 million on television ads in Georgia. Trump and the Republican National Committee, meanwhile, have spent more than $23 million on ads there.

Biden chose Warm Springs, Georgia -- the home of Franklin Delano Roosevelt's "Little White House," where he recovered from polio -- to deliver what his campaign characterized as his final argument in the 2020 race last Tuesday.

The speech underscored how -- even as the coronavirus pandemic has upended the campaign and American life -- Biden's central message has largely remained unchanged since he launched his campaign in April 2019, criticizing Trump on moral grounds.

"I believe this election is about who we are as a nation, what we believe, and maybe most importantly, who we want to be. It's about our essence; it's about what makes us Americans. It's that fundamental," Biden said.

This story has been updated with Obama's remarks in Atlanta.