EXCLUSIVE: A former White House physician-turned-Republican lawmaker says President Biden's mental fitness is a matter of "national security" 

"The article's just documenting what I've been saying all along: he's not fit to be the commander-in-chief," Rep. Ronny Jackson, R-Texas, told Fox News Digital on Wednesday. "He's got significant issues, he shouldn't have the job. You know, it's a national security issue for us."

It comes after a bombshell report in the Wall Street Journal that cited interviews with 45 people over the course of several months, claiming that congressional leaders and others who have met with Biden have noticed he "appears slower now" and is "someone who has both good moments and bad ones." 

Before being elected to Congress, Jackson served as the top White House physician to former Presidents Obama and Trump. He also served as chief medical adviser for the latter.

BIDEN SAYS WORLD LEADERS ARE SCARED OF ANOTHER TRUMP PRESIDENCY, TELL HIM 'YOU CAN'T LET' TRUMP WIN

The Journal's report has prompted furious pushback from the White House and its allies, who have dismissed it as a GOP-led hit piece.

However, Jackson pointed out that some of the commentary apparently came from Democrats. The report said, "Most of those who said Biden performed poorly were Republicans, but some Democrats said that he showed his age in several of the exchanges."

The Texas Republican speculated that it could be the beginnings of a political coup against the 81-year-old president.

"I think that the fact that it came out like this, and is so well sourced, tells me that this might be the left's first attempt to start laying the groundwork to get rid of him," Jackson said.

Jackson told Fox News Digital that he has sent five letters to the White House since Biden took office in January 2021, urging him to take a cognitive test and to make those results public. All five letters have gone unanswered, he said.

BIDEN ORDER TO BLOCK MOST ILLEGAL IMMIGRANTS WHEN CROSSINGS SURGE, AS ELECTION NEARS

"I don't know if it does any good to send another letter at this point," Jackson said. "They've ignored them all."

There have been several recent polls that show Biden's age is a top concern for voters.

A March New York Times/Siena College poll found that 61% of respondents who voted for Biden in 2020 agreed with the statement, "Joe Biden is just too old to be an effective president." 

White House spokesman Andrew Bates hit back at the Journal's report, saying, "Congressional Republicans, foreign leaders and nonpartisan national-security experts have made clear in their own words that President Biden is a savvy and effective leader who has a deep record of legislative accomplishment."

"Now, in 2024, House Republicans are making false claims as a political tactic that flatly contradict previous statements made by themselves and their colleagues," Bates said.

BIDEN SAYS TRUMP ‘SHOULD’ HAVE OPPORTUNITY TO APPEAL CONVICTION, GRINS AND IGNORES QUESTIONS

Speaker Emerita Nancy Pelosi, D-Calif., posted on X, "Many of us spent time with [the Journal] to share on the record our first-hand experiences with [Biden], where we see his wisdom, experience, strength and strategic thinking. Instead, the Journal ignored testimony by Democrats, focused on attacks by Republicans and printed a hit piece."

"I made clear to the [Journal] regarding the January meeting on Ukraine that the President was absolutely engaged & ran that meeting in a way that brought everyone together. I'm not quoted — I wonder why," Sen. Patty Murray, D-Wash., wrote on X.

Fox News Digital reached out to the White House for further comment.