“I encourage every American to give him a chance and lend him your support,” Mr. Obama said.
Representative James Clyburn of South Carolina, whose endorsement as the state’s Democratic primary approached was a key turning point in the race and a huge boost to Mr. Biden said his win “marks a new chapter for our country.”
“As we face unprecedented challenges, Americans have chosen you to lead us out of the chaos and to build a stronger community,” he wrote on Twitter. “Today, I am hopeful for a brighter future.”
Maya Harris, Ms. Harris’s sister, immediately invoked the memory of their mother, Shyamala, who the vice-president elect often discussed during the campaign when telling her back story and sharing her values. Julia Louis-Dreyfus, the actress who for years played a female vice president in the HBO comedy “Veep,” made sure to note: “‘Madam Vice President’ is no longer a fictional character.“
The Trump campaign, for its part, said it would continue to pursue its legal challenges, and Mr. Trump released a statement in which he said he would “not rest until the American People have the honest vote count they deserve and that Democracy demands.”
Newt Gingrich, the former Republican Speaker of the House and one of Mr. Trump’s staunchest supporters, baselessly insisted that the media had jumped the gun and declared a winner in the race before recounts had started and legal challenges had unfolded.
Senator Josh Hawley, Republican of Missouri, similarly objected to the presidential race call on Saturday. “The media do not get to determine who the president is. The people do. When all lawful votes have been counted, recounts finished, and allegations of fraud addressed, we will know who the winner is.”
But in one of the first statements to surface from a Republican lawmaker on Saturday, Representative Fred Upton of Michigan affirmed a Biden victory. “I am raising my hand and committing to working with President-elect Biden,” he said.
Senator Mitt Romney of Utah, the Republican presidential nominee in 2012, extended his own congratulations to Mr. Biden and Ms. Harris, conferring the titles “president-elect” and “vice president-elect” on them in his tweeted statement.
“We know both of them as people of good will and admirable character,” he said. “We pray that God may bless them in the days and years ahead.”
And Jeb Bush, the former governor of Florida who failed to defeat Mr. Trump in the 2016 Democratic primary, said it was time to “heal deep wounds” and added that he would be “praying” for Mr. Biden’s success.
The specter of a prolonged legal battle could not temper the enthusiasm of Democratic Party leaders who have known and worked with Mr. Biden for years.
Speaker Nancy Pelosi, in a statement, said that voters had “elected a unifier who values faith, family and community, and who will work tirelessly to heal our nation.” And Senator Chuck Schumer, the minority leader, said the American people had “placed their faith in Joe Biden and Kamala Harris” to confront challenges posed by the virus, the economy and global warming in the coming years.
In statement, Tom Perez, the chairman of the Democratic National Committee said that by electing Mr. Biden, “The American people chose hope” and “dignity and opportunity for all.”
“This is a historic victory,” he said.
“To the families of those who’ve lost loved ones to COVID-19, and to all our Americans yearning for change, our message is simple: You will finally get the leadership you deserve.”
And Hillary Clinton, the former Secretary of State and 2016 Democratic nominee who won the popular vote but ultimately lost to Mr. Trump, said voters had issued a “repudiation” of the president and offered a riff on one of her campaign slogans.
“Thank you to everyone who helped make this happen,” she said. “Onward, together.”