ATLANTA — President-elect Joseph R. Biden Jr. on Tuesday urged Georgia voters to cast ballots for two Democratic Senate candidates in a pair of critical runoffs early next month that he hopes will give his party control of the Senate and help Democrats advance the agenda he promised during his campaign.
“You all did something extraordinary in November,” Mr. Biden said to cheers and honks at a drive-in campaign rally intended to minimize the spread of the coronavirus. “You voted in record numbers in order to improve the lives of every Georgian. And you voted as if your life depended on it.”
“Well, guess what?” he added. “Now you’re going to have to do it again.”
Mr. Biden arrived in Georgia a day after the Electoral College affirmed his victory and in-person early voting began for the elections that will determine whether Republicans lose their majority in the Senate. Hours ahead of the event, Senator Mitch McConnell of Kentucky, the Republican leader, acknowledged Mr. Biden’s victory for the first time, saying “the Electoral College has spoken.”
To win control, Democrats need to defeat both of the state’s incumbent Republican senators, David Perdue and Kelly Loeffler, in contests that have drawn intense national attention and significant campaign cash. Mr. Perdue is facing Jon Ossoff, while Ms. Loeffler is being challenged by the Rev. Raphael G. Warnock, the senior pastor of Ebenezer Baptist Church in Atlanta.
The results of those two elections on Jan. 5 will have an outsize effect on the contours of Mr. Biden’s presidency. If Republicans keep both seats, the president-elect will face steeper challenges in securing confirmation for his cabinet and will most likely have to pare back his ambitions on climate change, immigration, infrastructure spending and other priorities.
The rally for Mr. Ossoff and Mr. Warnock was held on the grounds of Pullman Yard, a former rail car depot that became a popular site for film and movie shoots and will be redeveloped into retail and office space.
The site reflects the physical transformation Atlanta has undergone, where a surge in construction and development has stoked familiar worries about gentrification. But the transformation has also driven the political shift in Georgia that helped propel Mr. Ossoff and Mr. Warnock into the runoffs.
“It looks totally different than when I got here in ’96,” said Fantara Houston, an elementary school assistant principal who attended the rally.
The rallygoers — which spanned age and race and included Atlanta natives as well as transplants who have flooded into the city in recent years — watched from their cars, tooting their horns in place of applause. Another crowd of hundreds gathered along the sidewalks outside.
Fighting a cold and coughing several times during his remarks, Mr. Biden sought to tie Ms. Loeffler and Mr. Perdue to President Trump’s failed efforts to overturn the elections by raising false allegations of voting fraud in Georgia and other swing states.
Mr. Biden mocked the two senators for supporting a lawsuit filed by the Texas attorney general that sought to overturn the results of the presidential elections in four states, including Georgia.
“Maybe your senators were just confused. Maybe they think they represent Texas,” Mr. Biden said to more honks and cheers. “Well, if you want to do the bidding of Texas, you should be running in Texas, not in Georgia.”
In the five weeks since being projected to be the president-elect, Mr. Biden has sought to minimize partisanship and keep his focus on the pandemic, which has killed more than 300,000 people in the United States and is raging out of control. In speeches, he has repeatedly called for unity of purpose and said he will be a president for all Americans, including the more than 74 million who voted for Mr. Trump in the presidential race.
But for Mr. Biden, the runoff elections will be an early test of his power to shape the future of the Democratic Party.
In an email to his supporters as he flew to Atlanta from Washington, Mr. Biden made a raw, political appeal for campaign contributions to help the Democratic Party win.
“Both of these races are within a few points, and it really could go either way,” Mr. Biden wrote in the email. “That’s why I’m holding a rally today for both of these candidates, so they can spread their message to as many Georgians as possible. And if you donate $7 you can help them and the D.N.C. reach even more voters,” he said, referring to the Democratic National Committee.
Mr. Biden narrowly won Georgia last month, making him the first Democratic presidential candidate to carry the state since 1992.
“Our message and his message is going to continue to reflect what he’s been saying all along,” Jennifer O’Malley Dillon, Mr. Biden’s campaign manager and incoming deputy chief of staff, said of his visit. “In particular, really talking about early voting and the importance of voting, talking about the importance of Georgia in his victory.”
In his remarks, the president-elect singled out the contributions of Stacey Abrams, who lost a bid to become Georgia’s governor in 2018 but is credited by many Democrats in the state for energizing the electorate by continuing to campaign for voter rights in the past two years.
“Is there anyone in America who has done more to protect the right to vote in this election?” Mr. Biden asked the crowd. “Is there anyone who’s done more to make sure the voice of every Georgian is heard? I don’t think so. Stacey Abrams, you’re a hero.”
And he repeatedly urged Georgians not to wait until Jan. 5 to vote.
“Tell your friends, your family, just like you did in November,” he said. “Turn out the vote so that it’s not even close.”
Runoff elections typically see a substantial drop-off in voter interest, especially in comparison with a presidential campaign, but the first day of early voting suggested these high-stakes races were bucking that trend.
About 168,000 Georgia voters showed up to voting sites on Monday, exceeding by tens of thousands the number of votes cast on the first day of in-person early voting for November’s general election, suggesting voter interest stoked by Mr. Trump, Mr. Biden and their fired-up supporters.
Mr. Trump held a rally in southern Georgia this month, and on Tuesday, a spokesman for his campaign, Tim Murtaugh, sounded the same line of attack being used by Ms. Loeffler and Mr. Perdue. Mr. Ossoff and Mr. Warnock, he said, “represent the left-most fringe of the Democrat Party.”
A small group of Mr. Trump’s backers came to Mr. Biden’s event, waving large banners. Two of them walked on the street in front of the crowd, waving an American flag and wearing “Make America Great Again” hats.
One of Mr. Biden’s supporters, Nicole Gordon, brought her own small speaker and sang along as she played the Rolling Stones’ “You Can’t Always Get What You Want” — a not-so-subtle jab. Later, she held her speaker over her head, singing along to Aretha Franklin’s “Respect.”
Rick Rojas reported from Atlanta, and Michael D. Shear from Washington. Glenn Thrush and Thomas Kaplan contributed reporting from Washington.