US President Joe Biden has announced he will end his re-election campaign, saying it is “in the best interests of the party and the country”.

The shocking announcement, just four months before Americans go to the polls, has completely changed the race for the White House.

President Joe Biden, 81, has come under intense pressure from voters and Democrats after a disappointing debate performance in which he faltered in his speech against former President Donald Trump in late June.

Following the announcement on Sunday evening, President Biden endorsed his running mate, . He said his “first decision as the party’s nominee in 2020” was to pick Harris, saying it was “the best decision” he had ever made.

In a letter posted on his social media account X announcing his withdrawal from the presidential race, Mr. Biden wrote that serving as president was the greatest honor of his life.

Mr Biden added that he would be “focused solely on fulfilling my duties as President for the remainder of my term”.

Calls for Mr Biden to drop out of the White House race began to mount after his disastrous debate performance in late June against former President Donald Trump.

During the debate, he was criticised for his incoherent speech and weak voice – which his party blamed on the flu.

There were growing calls within the party for him to step aside, and a growing number of party members feared his campaign would hurt their own re-election chances in November.

Several senators in the Senate have also called on him to withdraw.

Less than two weeks ago, President Biden held a summit with NATO leaders, aware that he would face intense scrutiny following his debate performance.

The incident did little to ease tensions within his party, as he mistakenly referred to Ukrainian President Volodymyr Zelensky as “President Putin” and appeared to refer to Vice President Harris as “Vice President Trump.”

Although Kamala Harris has received Joe Biden’s support, it is currently unclear whether she will be selected as a replacement candidate.

After news of Mr Biden’s withdrawal broke on Sunday evening, the BBC’s US partner CBS reported that the Democratic National Committee was holding an emergency meeting.

The focus now will be on the Democratic National Convention taking place next month in Chicago.

Mr Biden has swept the primaries, meaning each state’s representatives at the convention have pledged to vote for him – though they could now vote for another candidate.

‘Gratitude from the bottom of my heart’

In his statement, President Biden thanked Vice President Kamala Harris, saying she has been an “extraordinary partner.”

“And let me express my heartfelt gratitude to the American people for the trust and confidence you have placed in me,” his statement read.

“I believe today and forever there is nothing that America cannot do – when we do it together. We just have to remember that we are the United States of America.”

He wrote that he would address the nation on the issue next week.

He returned to his home in Delaware last week after being diagnosed with Covid, but said on Friday he was looking forward to “getting back on the campaign trail next week.”

He previously said that only “Almighty God” could make him withdraw from the race, but later said he would consider stopping his candidacy if he had health problems.

Reacting to the news, on his Truth Social platform, Donald Trump said that Joe Biden “is not fit to run for president”.