A moderate House Democrat said President Biden's White House tenure must "come to an end" on Thursday, the most significant voicing of opposition to his leadership from a member of his own party so far.

Rep. Marie Gluesenkamp Perez, D-Wash., previously said she believed Biden would lose to Trump, but now she is the 15th congressional Democrat to call on the president to end his re-election bid.

"I’ve spent the past two weeks listening to my constituents express their concerns about the President’s age and health," she said in a statement to local outlet KGW, an NBC affiliate.

"Americans deserve to feel their president is fit enough to do the job. The crisis of confidence in the President’s leadership needs to come to an end. The President should do what he knows is right for the country and put the national interest first."

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Gluesenkamp Perez is one of the most vulnerable Democrats of this election cycle and has frequently broken from her own party on votes.

Biden, meanwhile, is fighting for his political life in the wake of his disastrous debate performance against former President Trump late last month.

Biden spoke with a hoarse voice, which he attributed to a cold, and stumbled over his answers several times during the primetime event. Viewers also observed him appearing tired and noticeably less sharp than he looked the last time he faced Trump in 2020.

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It spurred concerns among members of his party that he would lose to Trump in November and may not be fit to serve another four years.

Gluesenkamp Perez told KATU after the debate, "About 50 million Americans tuned in and watched that debate. I was one of them for about five very painful minutes. We all saw what we saw, you can't undo that, and the truth, I think, is that Biden is going to lose to Trump."

Biden, for his part, has maintained several times that he is not budging. 

Gluesenkamp Perez's statement comes just a few hours before Biden's 6:30 p.m. Eastern Time press conference. It's a pivotal event for the president as he seeks to fight back doubts that he's not physically or mentally fit for the White House.

House Democrats left Capitol Hill around noon on Thursday to return to their districts for a week-long break. 

Before that, left-wing lawmakers spent the week huddled as both a caucus and in smaller groups to discuss the path forward for Biden. 

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House Democratic Leader Hakeem Jeffries, D-N.Y., who has said he is behind the presidential ticket, told reporters earlier Thursday that he did not believe Biden was a drag on vulnerable Democrats.

"House Democrats are engaged in conversations with House Democrats at this moment in time. Those conversations have been candid, clear eyed and comprehensive, and that's important for us to do as a House Democratic caucus family. And as long as those conversations are ongoing, I'm going to respect the sanctity of those conversations until we conclude that process," he said.