Vice President Kamala Harris wasted no time launching her 2024 presidential campaign, seeking the support of fellow Democrats with the backing of President Joe Biden after he pulled out of the race amid concerns about his age and health.

Her campaign officials and allies made hundreds of calls on behalf of Harris on Sunday, urging delegates to the Democratic Party convention next month to join in nominating her for president in the Nov. 5 election against Republican Donald Trump.

Multiple sources said the calls, aimed at blocking would-be Democratic challengers, began almost immediately after the 81-year-old Biden abandoned the race.

At the same time, Democratic state party chairs backed Harris in a phone call, several participants said.

Harris spoke with Pennsylvania Governor Josh Shapiro, a potential vice presidential running mate, House Democratic leader Hakeem Jeffries, and Congressional Black Caucus chair Representative Steven Horsford, said a source familiar with the matter.

Harris, a 59-year-old woman who is Black and Asian-American, would fashion an entirely new dynamic with Trump, 78, offering a vivid generational and cultural split-screen.

The United States has yet to elect a woman president in its 248-year history.

"Harris will be easier to beat than Joe Biden would have been," Trump asserted on CNN shortly after Biden's announcement.

Biden, the oldest person ever to have occupied the Oval Office, said he would remain in the presidency until his term ends on Jan. 20, 2025, while endorsing Harris to run for president in his place.

The White House said Harris would deliver remarks on the South Lawn at 11:30 a.m. ET (1530 GMT) on Monday at an event celebrating the NCAA 2023-24 college championship teams.

Facing mounting questions about his mental acuity, Biden is the first sitting president to give up his party's nomination for reelection since President Lyndon B. Johnson during the Vietnam War in March 1968.

Biden's withdrawal leaves his replacement with less than four months to wage a campaign. Prominent Democrats, including potential Harris challengers such as California Governor Gavin Newsom, immediately backed the vice president.

"My intention is to earn and win this nomination," Harris said in a statement. "I will do everything in my power to unite the Democratic Party — and unite our nation — to defeat Donald Trump."

Despite the early show of support for Harris, talk of an open convention when Democrats gather in Chicago Aug. 19-22 was not totally silenced.

Former House Speaker Nancy Pelosi and former President Barack Obama did not announce endorsements, although both praised Biden.

Two other potential challengers - Michigan Governor Gretchen Whitmer and Kentucky Governor Andy Beshear - made no mention of the vice president in their statements.

With Democrats wading into uncharted territory, Democratic National Committee Chair Jaime Harrison said the party would soon announce the next steps in its nomination process.

What is certain is that Biden's withdrawal has again reshaped a White House contest shaken repeatedly during the last month.

On June 27, Biden's poor performance in a debate with Trump led many Democrats to urge him to drop out. Then on July 13, a gunman attempted to assassinate former President Trump.

And last week Trump named hardline Republican U.S. Senator J.D. Vance, 39, to serve as his vice presidential running mate.