Former assistant U.S. attorney Andy McCarthy on Monday called for 25th Amendment hearings on President Biden after his very shaky performance at last week's presidential debate left brand-new questions about his mental acuity and ability to carry out his duties, warning that the "threat" environment today bears resemblance to "right before 9/11."

McCarthy, a Fox News contributor, made the comment on "Outnumbered" after he was asked about a pattern of concerning behavior by the president, including his disastrous debate performance last Thursday. The president was seen visibly confused at times, mouth agape, and frequently unable to complete sentences.

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"I think it’s time to have 25th Amendment hearings," McCarthy said. "I don’t really care that much about the campaign when it comes to this issue…I started to prosecute jihadists back in the 1990s. The ‘threat’ environment we are in today is reminiscent of right before 9/11, except right before 9/11 we didn’t have war raging in Europe and the Middle East, where Israel is looking at a 2-front war now. It is crazy to have someone who is non compos mentis (loose translation: ‘of unsound mind’) president."

Rep. Chip Roy (R-Texas) introduced legislation last week that would urge Vice President Kamala Harris to bring together executives of Biden's Cabinet and jointly declare Biden unfit to continue as president.

Roy introduced the resolution on Friday, calling on Vice President Kamala D. Harris to "convene and mobilize the principal officers of the executive departments of the Cabinet to activate section 4 of the 25th Amendment to declare President Joseph R. Biden incapable of executing the duties of his office and to immediately exercise powers as Acting President."

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The resolution claims that Biden "has repeatedly and publicly demonstrated his inability to discharge the powers and duties of the Presidency, including, among others, the powers and duties of the Commander-in-Chief."

Section 4 of the 25th Amendment authorizes the vice president and a majority of the executive Cabinet to make the decision whether the president is fit to continue in office or not. The vice president could assume the presidency if the president is declared unfit for office by her and a majority of the president's Cabinet or Congress. 

"There’s a lot of people asking about the 25th Amendment, invoking the 25th Amendment right now, because this is an alarming situation," House Speaker Mike Johnson said on Friday." Our adversaries see the weakness in this White House as we all do. I take no pleasure in saying that. I think this is a very dangerous situation."

Biden has faced severe backlash in the days following the debate, with many prominent Democrats and left-leaning pundits calling for him to drop out of the race over concerns about his mental fitness and ability to withstand his opponent.

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There have also been reports of concerned donors and Democratic Party "panic" over his performance, but the campaign has thus far held firm that Biden, who already clinched the delegates necessary to win the 2024 nomination, isn't going anywhere.

Biden's campaign tried to explain his performance by saying he had a cold the night of the debate. Supporters of the president have conceded he had a "bad night" but argue that 90 minutes of a bad performance does not negate the accomplishments of his presidency.

Former President Obama conceded that Biden failed to deliver a strong showing but took a shot at Trump while defending his former vice president.

"Bad debate nights happen. Trust me, I know. But this election is still a choice between someone who has fought for ordinary folks his entire life and someone who only cares about himself," he wrote on X.

Fox News' David Rutz and Timmothy Nerozzi contributed to this report.