As doubts grow about President Biden’s mental acuity, the spotlight turns to whether he can step down as the presidential nominee while completing his first term, and what that would mean for Vice President Kamala Harris’ political future.

‘Vice President Kamala Harris owes the American people an explanation as to why she has not been honest about President Biden’s steep decline into incapacity,’ Mike Howell, executive director of the conservative advocacy group Heritage Action, told Fox News Digital.

‘She chose politics over national security and history will judge her for that decision.’

Howell added that Democratic lawmakers are unlikely to call for Biden to retire immediately and allow Harris to take the helm, because ‘to admit that is that they’ve basically been complicit in a lie for the last three and a half years,’ referring to Biden’s declining health.

‘Him stepping down is an implicit endorsement of Kamala Harris being the nominee, because she would be the incumbent president at that point, and so I think that factors into it,’ Howell said. ‘What’s happening right now is there’s just going to be a series of rounds of people increasingly calling for it, and obviously President Biden’s trying to resist those calls as much as possible. But I think it’s unavoidable that more and more do call.’

Despite the growing chorus of concerned lawmakers calling on Biden to suspend his re-election campaign due to his poor debate performance and fading vitality, Biden has repeatedly said he is not dropping out of the race.

‘Most of the Democrats who are questioning whether or challenging President Biden should run are in either swing districts or tough re-election races of their own, or they need independent and Republican votes,’ Democratic strategist Mustafa Rashed told Fox News Digital in an interview.

‘It’s tough,’ Rashed continued. ‘The advantage that the vice president has is that she’s been adjacent to the Oval Office for the last three and a half years, which is something that no one else can say. I would also say that she’s the only person that’s been nationally, publicly and thoroughly vetted right now, like some of the other candidates have not gone through the sort of vetting process that’s required to run for national office.’

Other potential Democratic candidates who have been floated as options to replace Biden include Gov. Gavin Newsom, of California, and Gov. Gretchen Whitmer, of Michigan.

When asked at a Biden-Harris campaign event in New Hampshire this week, Newsom said Harris would likely win in a hypothetical matchup against former President Trump. 

‘I have no doubt about that. And that’s from someone that’s also known her longer than most, before we were both in politics,’ Newsom said, The Associated Press reported. ‘But I don’t expect it’s going to come to that.’

Democrats also met behind closed doors Monday as pressure mounted on Biden to drop out of the race. 

Fox News learned that multiple Democrats on House committees expressed concerns about the viability of Biden continuing to run for re-election against Trump after House Minority Leader Hakeem Jeffries, D-N.Y., held a virtual meeting with ranking Democrats on House panels Sunday afternoon.

Fox is told the consensus among most Democrats on the call who suggested Biden should abandon the race was that the party should focus on Harris as a potential successor.

Additionally, a recent CNN/SSRS poll shows Harris performing slightly better than Biden in a matchup against Trump.

House Republicans are already on the offense against Harris as a possible replacement for Biden’s candidacy should he step down from the race.

GOP lawmakers – in both safe red seats and swing districts being targeted by the left – dismissed Harris as a political threat to their chances in November, arguing she’s still tied to the same progressive Biden policies they believe are unpopular with voters.

Rep. Nick Langworthy, R-N.Y., who served as longtime chair of the New York Republican Party before coming to Congress, previously told Fox News Digital, ‘Kamala Harris is just as responsible for this administration’s failures, but she’s more incompetent.’

A swing-seat Republican who asked not to be named told Fox News Digital they were skeptical Harris would do better on the debate stage than Biden. 

‘I would say she’s the weakest part of the ticket right now, as bad as Biden is,’ that GOP lawmaker said.

Reps. Jerrold Nadler, D-N.Y., Mark Takano, D-Calif., Don Beyer, D-Va., and Adam Smith, D-Wash., reportedly expressed privately that Biden should exit the presidential race as the Democratic nominee on Sunday. Most of them also reportedly said Harris should be the nominee, two people familiar with the meeting told The Associated Press. 

Following reports on the meeting, Beyer issued a statement saying he backs the president staying in the race. 

‘I support President Biden. I support the Biden-Harris ticket, and look forward to helping defeat Donald Trump in November,’ the representative said. ‘I was proud to host an event this week in Northern Virginia with the President, and will continue doing all I can to support the Biden-Harris campaign in Virginia and across the country.’

Fox News’ Elizabeth Elkind, Greg Wehner and Chad Pergram contributed to this report.