Watch: Joe Biden 'zones out' mid-interview when asked about possible 2024 presidential bid

Joe Biden appeared to zone out mid-interview and faltered in his response when asked whether his wife wants him to run again in 2024, renewing concerns over the US president's age.

Mr Biden, 79, sidestepped a question about the members of the public who believed he should not run again because of his age.

"The only reason to be involved in public life is: Can you make life better for other people" he replied, and going on to suggest he had an "obligation" to do so.

When asked if his wife, First Lady Jill Biden, supported him seeking re-election, Mr Biden nodded, then paused and appeared to lose his train of thought during the MSNBC interview.

The silence prompted interviewer Jonathan Capehart to prod Mr Biden, saying: "Mr President?" The president ultimately provided a faltering response. He said: "Dr Biden thinks that uh, my wife thinks that uh, that I uh, that, that we're, that we're doing something very important and that I shouldn’t walk away from it".

The clip was swiftly shared by the Republican National Committee, which has proved adept at sharing short, viral clips of Mr Biden's verbal stumbles.

During the Friday night interview, Mr Biden also repeated his previous comments on seeking re-election, stressing that he would not yet make a formal declaration, which would trigger campaign finance laws.

He added: "I have not made that formal decision but it's my intention to run again." The interview may have done little to allay concerns over his fitness for high office. He will become the first octogenarian US president next month.

With his approval rating underwater in polls, Mr Biden has held back from the campaign trail ahead of the midterm elections.

But he warned voters that Republicans could upend his administration's legislative victories in Congress if they seize control after November 8.

"They don’t have a platform other than to tear down what I’ve been able to do, we’ve been able to do," he said.

Mr Biden also weighed in for the first time on the subpoena the House January 6 Committee has issued for his predecessor.

Mr Biden said it would "make sense" for Donald Trump to comply with a subpoena to testify, a historic action Congress has only taken on former US presidents twice before.

The panel, which is investigating the deadly Capitol riot on Jan 6, 2021, demanded Mr Trump give evidence under oath in relation to his role in the attack. If he fails to do so it could ultimately lead to criminal charges and a jail sentence.

In his first comments on the subpoena, Mr Biden told MSNBC that he was "not going to opine on what he (Trump) should do."

But asked whether Mr Trump should comply with the request, he responded: "it seems to me that would make sense." "I think the committee's handled it very well."