President Biden's 81st birthday ushered in even more conversations surrounding his age and declining cognitive acuity, two things Texas Republican Rep. Ronny Jackson, a former White House physician, believes are valid causes for concern.

"[The decline is] happening quickly," Jackson told "Sunday Morning Futures" guest anchor Sean Duffy.

"Like you said, I've taken care of three presidents… so I know firsthand what it takes to be the commander-in-chief and the head of state. It's a grueling job, both mentally and physically. This man can't do the job. He's proven to us every single day that he can't do the job, but this is going to get worse."

BIDEN DOES NOT HAVE ‘COGNITIVE ABILITY’ TO SERVE ANOTHER TERM, SAYS FORMER WH DOCTOR

President Joe Biden

President Biden clears his throat as he announces new steps requiring government to buy more made-in-America goods during remarks on March 4, 2022.  (REUTERS/Evelyn Hockstein)

Jackson served as a physician under the Bush, Obama and Trump administrations and has previously sounded the alarm over Biden's cognitive acuity, even demanding he take a cognitive test or drop out of the 2024 race.

Jackson said the decline has been evident for some time, looking back on Biden as a candidate before his 2020 match-up against then-president and current Republican frontrunner Donald Trump, whom Jackson has endorsed for their 2024 rematch.

"It's just unbelievable how much he's degenerated just during his time in office. We cannot afford to have this man in office for the remainder of this term and then [for] another four years after that. He's already putting us at great risk right now," he said.

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Meanwhile, young voters lament the president is "out of touch" with everyone as his support among Gen Z voters – a crucial demographic for Democrats – erodes in recent polls.

One recent NBC News poll, for instance, indicated that Trump leads Biden by four percentage points among registered voters between the ages of 18 to 34.

Though prominent names like California Gov. Gavin Newsom or former First Lady Michelle Obama have been tossed around in speculation while many caution against letting Biden serve as the Democratic nominee, a potential replacement for him remains unclear.

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Gov Gavin Newsom

California Gov. Gavin Newsom, a Democrat, has been touted as a viable alternative to Biden in 2024, but has denied any rumors he intends to run. (California Governor Gavin Newsom YouTube channel)

Jackson, continuing his discussion with Duffy, listed a series of concerns he has with the direction of the country, pointing to the crisis at the southern border, international tensions and the economy.

"[Look at] the wars that we're getting drawn into. Things that wouldn't happen if Donald Trump were there because our enemies don't fear us anymore. They have no respect for us anymore and our adversaries don't trust us anymore, and it's because we don't have the leadership in the White House that we need," he said.

"It's because this man, even if he wanted to, he cannot provide that leadership. He is not physically and cognitively fit for office anymore, and somebody in his inner circle needs to step up to the plate and make him aware of this, and he needs to move on for the safety and security of this country."

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