Dr Jackson, who speaks with Mr Trump a few times a day and travels with him, said he did not think the USA president needed cognitive testing based on medical guidelines - but added the 30-question Montreal Cognitive Assessment at Mr Trump's request.
But Jackson, who served as the White House physician since 2013, found allies in former Obama officials who called him a "saint" and "a phenomenal doctor". It is a well-known and well-tested assessment that doctors can quickly use to detect "mild cognitive dysfunction", according to the test instructions.
According to Michael Wolff, author of Fire and Fury: Inside the Trump White House, all of the president's White House aides see him as a "child" who needs "immediate gratification".
Past presidents are not known to have been tested for mental acuity while in office including Ronald Reagan who five years after leaving the White House in 1989 was diagnosed with Alzheimer's disease, an incurable, degenerative brain condition.
Dr Jackson performed a series of tests on the 71-year-old president on Tuesday as part of his first medical exam in office. The patient is asked to draw a clock and put numbers on it, and to draw a cube.
It's designed, he explained, to test for "minimum cognitive function to be able to do important things" and "does not absolutely assess personality issues".
Trump answered all 30 questions correctly, Jackson said. Jackson said he'd be arranging to have a dietitian consult with the White House chef to cut calories and would be recommending a low-impact, aerobic exercise program for Trump, with the aim of shedding 10 to 15 pounds this year. But he also added an extra exam - a cognitive screening test for memory loss or early dementia. It is "just one measure in a clinical judgment", he said in an email.
"Many of you may have picked up on the fact that we did do a cognitive assessment", Jackson said.
The White House, in an attempt to dispel concerns about Donald Trump's mental state, is highlighting the results of a test developed by a Canadian immigrant from Lebanon.
Jackson said on Tuesday that Trump asked him to perform the cognitive exam, which the doctor had not planned to do, having deemed it unnecessary.
He said despite the president's love of fast food and lack of exercise he was in good health, and that he has "incredible genes". Could you? Take a short version of the test above.
Jackson said that Trump's cholesterol level has jumped to 223, in the elevated range, and his low-density lipoprotein of 143 is borderline high, so he is increasing Trump's medication.
Jackson said that there is no reason Trump wouldn't be able to complete his first term healthwise, in addition to a second term if re-elected.
"This was a bit of a snapshot in time", she said.