WASHINGTON — President Biden will address the nation at 8 p.m. Wednesday about his decision to abandon his campaign for a second term amid mounting questions about his mental acuity.

“Tomorrow evening at 8 PM ET, I will address the nation from the Oval Office on what lies ahead, and how I will finish the job for the American people,” Biden, 81, tweeted Tuesday.

The president hasn’t been seen in public since last Wednesday when he traveled to his Delaware vacation home to recuperate from COVID-19 and is expected to return to the White House Tuesday afternoon.

Biden has insisted that he will serve the remainder of his term, which ends in January, as leading Republicans including House Speaker Mike Johnson of Louisiana call on him to resign.

Biden on Sunday evening endorsed Vice President Kamala Harris to replace him atop the Democratic ticket in the Nov. 5 election.

His abrupt retirement announcement followed a groundswell of calls from fellow Democrats for him to step aside after he appeared confused and made bizarre remarks such as that he “finally beat Medicare” at a June 27 debate against former President Donald Trump.

Biden had resisted calls to drop out, but ultimately relented just days before Democratic delegates were due to virtually nominate him.

“The name has changed at the top of the ticket, but the mission hasn’t changed at all,” Biden told campaign workers Monday in a speaker phone call to headquarters — speaking with a slurred, raspy voice.

“And by the way, I’m not going anywhere. I’m gonna be out there on the campaign with her, with Kamala. I’m going to be working like hell, both as a sitting president, getting legislation passed, as well as in campaigning,” Biden said.