“My fellow Democrats, I have decided not to accept the nomination and to focus all my energies on my duties as President for the remainder of my term”, Biden wrote on X Sunday.

Incumbent Biden backed his vice president Kamala Harris to replace him as the Democratic nominee, calling on his party members to “come together” to beat Republican Donald Trump.   

“My very first decision as the party nominee in 2020 was to pick Kamala Harris as my Vice President. And it’s been the best decision I’ve made. Today I want to offer my full support and endorsement for Kamala to be the nominee of our party this year. Democrats — it’s time to come together and beat Trump. Let’s do this.”

Biden, 81, has been facing calls from Democrats to step aside as their nominee following his disastrous performance at a debate with Trump on June 27.

Concerns have been growing about Biden being mentally unfit for president and compete with Trump, after he made a series of gaffes at a NATO summit earlier this month and a key press conference at the White House afterward.

Biden’s decision to drop out of the presidential race comes four months before election day in the US in November.  

Former president Trump, 78, formally accepted the GOP nomination for president at the Republican National Convention on July 18.