Dr. Ronny Jackson, the former White House physician, called on President Biden to immediately undergo a cognitive test so the commander-in-chief can prove to the American public sound mental capabilities. 

"We can't sit on this any longer," Jackson told "Hannity" Thursday night, citing Biden's "embarrassing" performance overseas this week with world leaders. 

"He's not physically or cognitively fit to be our president right now," Jackson added.

The freshman Texas congressman and 13 of his GOP colleagues sent a letter to Biden Thursday expressing "concern" with his cognitive state and cited several examples of potential memory lapses, including apparently forgetting the name of his Defense Secretary, telling an Amtrak story with a timeline that didn't add up and seemingly blanking on the often-quoted first line of the Declaration of Independence. 

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"Unfortunately, your mental decline and forgetfulness have become more apparent over the past 18 months," Jackson and the GOP reps wrote in a letter to Biden, the White House physician and Dr. Anthony Fauci. 

"We encourage you to follow the example set by President Trump by undergoing a cognitive test as soon as possible and immediately making the results available for the American people," the members of Congress added.

A White House spokesperson declined to comment late Thursday, but in May the White House said Biden would be going for a medical checkup this year and would be transparent about the results.

"The President is planning to have a checkup later this year, and the results will be released to the public," White House spokesman Andrew Bates told Fox last month. 

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Jackson, who was subject to his own Inspector General investigation in March that found he "disparaged" and "belittled" subordinates and engaged in "inappropriate conduct" involving alcohol use, was Trump's White House physician and his unsuccessful nominee in 2018 to become the Secretary of Veterans Affairs. At the time, Jackson faced enormous pressure to administer a cognitive test to Trump as pundits and mental health professionals openly speculated that the Republican could have early-stage dementia or a decline in mental health.

Trump scored a perfect 30 out of 30 during the cognitive test as part of his annual physical and Jackson announced the results in 2018 at a White House press conference, where he also famously quipped that Trump might "live to be 200 years old."

WASHINGTON, DC -  Then-White House physician Dr. Ronny Jackson speaks to reporters during the daily briefing in the Brady press briefing room at the White House in Washington, DC on Tuesday, Jan. 16, 2018. Jackson is now calling for President Biden to undergo a cognitive exam. (Photo by Jabin Botsford/The Washington Post via Getty Images)

Jackson has long called for Biden to take a similar test but now he has the backing of several of his GOP House colleagues in arguing the American people deserve to have "absolute confidence" in their president's ability to perform the duties of the office. 

"I would argue that the American people don’t have that confidence in President Biden," Jackson said in a statement. 

The lawmakers urged Biden to follow the same example as Trump and take the Montreal Cognitive Assessment (MOCA). 

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"Given the precedent set and Biden’s clear mental impairment, I believe it is past time he undergo a cognitive test," Jackson said. 

Other GOP House members signing the letter were Reps. Bob Gibbs of Ohio, Jeff Duncan of South Carolina, Andy Harris of Maryland, Brian Babin of Texas, Jody Hice of Georgia, Claudia Tenney of New York, W. Gregory Steube of Florida, Tom Tiffany of Wisconsin, Kat Cammack of Florida, Jerry L. Carl of Alabama, Pat Fallon of Texas, Diana Harshbarger of Tennessee and Beth Van Duyne of Texas.