Sen. Patty Murray, D-Wash., third in line to the presidency, said President Biden must "seriously consider" how to secure his legacy for the future as calls grow among Democrats for Biden to drop out of the 2024 presidential race over concerns about his mental fitness.

Murray, who as president pro tempore is third in line to the presidency, said in a statement on Monday that Biden needs to be "more forceful and energetic" on the campaign trail to prove to voters that he is more fit for another term in the White House than former President Trump.

"President Biden has to lead the charge in making that case," Murray said.

"We need to see a much more forceful and energetic candidate on the campaign trail in the very near future in order for him to convince voters he is up to the job," Murray said. "At this critical time for our country, President Biden must seriously consider the best way to preserve his incredible legacy and secure it for the future."

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Sen. Patty Murray

Sen. Patty Murray said President Biden must show voters a "much more forceful and energetic" candidate on the campaign trail. (Reuters/Jon Cherry)

Biden's physical and mental fitness were called into question after the first presidential debate in June, sparking calls from voters, Democratic members of Congress and donors for the party to select a new nominee to take on Trump in November.

President Joe Biden

President Biden has remained defiant against calls to step down from the 2024 presidential race. (AP Photo/Susan Walsh)

House Democrats held a virtual meeting over the weekend to discuss the future of Biden's re-election campaign in the wake of his highly-criticized performance at the debate.

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Biden, however, has remained defiant against all calls to step aside, proclaiming that he will be staying in the race.

"The bottom line here is that we’re not going anywhere. I am not going anywhere," Biden said during a call into MSNBC’s "Morning Joe" on Monday.

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"I wouldn’t be running if I didn’t absolutely believe that I am the best candidate to beat Donald Trump in 2024," Biden said. "We had a democratic nominating process where the voters spoke clearly. I won 14 million of those votes."

Fox News’ Aubie Spade and Nikolas Lanum contributed to this report.