"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 continued.
The freshman Texas congressman and 13 of his GOP colleagues addressed a letter to Biden Thursday showing "concern" with his cognitive state and cited many instances of possible memory lapses, including apparently forgetting the name of his Defense Secretary, telling an Amtrak story with a timeline that didn't add up and apparently 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 continued.
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A White House spokesperson refused to comment late Thursday, though in May the White House said Biden would be going for a medical checkup this year and would be transparent regarding 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 explained last month.
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Jackson, who was subject to his own Inspector General investigation in March that discovered 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. Back then, Jackson faced tremendous stress to administer a cognitive test to Trump as pundits and mental health professionals openly thought that the Republican could have early-stage dementia or decay in mental health.
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Trump secured a perfect 30 out of 30 throughout the cognitive test as part of his annual physical and Jackson published the results in 2018 at a White House press conference, where he further famously quipped that Trump might "live to be 200 years old."
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Jackson has long called for Biden to take a similar test though now he has the backing of many 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.
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