President Joe Biden on Wednesday said abandoning his reelection campaign and endorsing his vice president, Kamala Harris, as the Democratic candidate was the best way to unite the country and save democracy, despite his ambition to win a second term.

Biden's announcement to end his presidential bid on Sunday followed a disastrous June debate with Donald Trump, which exacerbated questions about his ability to defeat the Republican candidate, or to serve another four years if he succeeded.

In his address to the nation from the Oval Office, the 81-year-old president said he believed he deserved to be reelected based on his record during his first term.

"But nothing, nothing can come in the way of saving our democracy. That includes personal ambition," he said. "So I decided the best way forward is to pass the torch to a new generation. That is the best way to unite our nation.”

In a post on his Truth Social platform, Trump said the speech was "barely understandable and sooo bad!"

In the three days since Biden's decision, Harris has pulled in broad support across the Democratic Party and revitalized its election campaign. Harris, the first Black woman and Asian American to serve as vice president, would become the first woman elected president if she prevails on Nov. 5.

Biden praised Harris, 59, as a strong leader who would make an effective president.

"She's experienced, she's tough, she's capable. She's been an incredible partner to me and a leader for our country. Now the choice is up to you the American people," he said.

Hours earlier, Trump tried to quash some of that momentum in an aggressive speech at a campaign rally, his first since Harris' emergence changed the race. "She is a radical Left lunatic who will destroy our country if she ever gets elected," he said.

Trump routinely uses insults in attacking his opponents and made clear he planned to ignore advice that he take a softer line. "I'm not gonna be nice!" he told his cheering supporters in Charlotte, North Carolina, a battleground state where voting preferences can swing to either side.

The combative tone of his speech was a strong signal that three months of bare-knuckled campaigning lay ahead.

At her first campaign rally since Biden's endorsement, Harris on Tuesday showed her willingness to counter-punch, comparing her background as a prosecutor to his record as a convicted felon.

"Do we want to live in a country of freedom, compassion and rule of law, or a country of chaos, fear and hate?," she asked during the speech in Milwaukee.

At Trump's rally, the former president attacked Harris as a driving force in the Biden administration who should be held responsible for its policies on immigration and other issues.

"As border czar, Kamala threw open our borders that allowed 20 million illegal aliens to stampede into our country from all over the world," said Trump, coming off a triumphant week in which his party unified around his presidential bid after a failed assassination attempt two weekends ago.

"I will terminate every single open border policy of the Biden-Harris administration and we will seal the border and we will stop Kamala Harris invasion without delay," he said.

Biden put Harris in charge of working with countries in Central America to help stem the tide of migration, but she was not given responsibility for border security nor was she named "border czar." She also has said she opposes open borders.

'PASS THE TORCH'

Biden, who for weeks resisted pressure from fellow Democrats to step aside, said in his address that he intended to focus on his work as president in the six months left in his term.

"That means I will continue to lower costs for hard-working families and grow our economy. I will keep defending our personal freedoms and our civil rights – from the right to vote – to the right to choose,” he said, outlining some themes that Harris is expected to build her campaign around.

The president returned to Washington on Tuesday afternoon after isolating with COVID at his home in Delaware, where he made the announcement that he was ending his campaign.

The Democratic National Committee's rules committee agreed on Wednesday on a plan to formally nominate Harris as soon as Aug. 1 - before the party's Aug. 19-22 convention in Chicago - with Harris picking a running mate by Aug. 7.

The Harris campaign on Wednesday said it has raised $126 million since Sunday, with 64% of donors making their first contribution of the 2024 campaign.

Earlier, the 59-year-old vice president called on a rally of more than 6,000 Black women in Indianapolis to help her revitalize the Democratic campaign.

Harris spoke at an event hosted by the Zeta Phi Beta Sorority, which was founded at Howard University, the historically Black college she attended. She hopes to tap sororities' multi-generational network of Black women - who played an important role in Biden's 2020 victory - to deliver strong voter turnout for Democrats again in November.

"I thank you. And now, in this moment, our nation needs your leadership once again," Harris said.

Harris and Trump are running neck to neck, public opinion polls showed this week.

A Reuters/Ipsos poll completed on Tuesday showed Harris with a marginal two-percentage-point lead over Trump, 44% to 42%. A CNN poll conducted by SSRS showed Trump leading Harris, 49% to 46%. Both findings were within the polls' margins of error.