Members of the press pushed Jackson on the president's mental health, exercise routine, waist size, diet, and how much longer he has to live.
Asked about a pre-emptive strike against North Korea - "a limited, pre-emptive attack to show the North that the United States means business", Reuters wrote - Trump said: "We're playing a very, very hard game of poker and you don't want to reveal your hand". Lindsey Graham, R-S.C., used "tough language" in response to Trump.
"I found no evidence that the president has any issues whatsoever with his thought process", Jackson told reporters during Tuesday's White House briefing.
It's one of several quick tests that can screen people for MCI or dementia. Test-takers are also asked to copy a simple line sketch of a cube; match the letter A to the number 1, the letter B to the number 2 and so on. It does not test for psychiatric fitness.
The doctor describes Trump as "very sharp" and "very articulate when he speaks to me".
Dr Ronald Petersen, an Alzheimer's expert at the prestigious Mayo Clinic, said he could not comment specifically on the president's cognitive health.
However, though Trump got a flawless score in the cognitive test, Jackson did admit that Trump could do better if he lost a few pounds, and said that he has a bit of high cholesterol. It is "just one measure in a clinical judgment", he said in an email.
The 6-foot-3 Trump weighed 107 kilograms, and his body mass index, or BMI, of 29.5 put him in the category of being overweight for his height.
Trump is the first president to undergo the memory screening, Jackson said.
Jackson, the White House physician, said Tuesday that Trump scored a flawless 30 out of 30 on the test. The doctor said he would also design a daily exercise program for Trump. We're going to continue to work on that, make that even healthier. Jackson said that Trump's blood pressure is 122 over 74.
Washington had been abuzz in recent days with details from a tell-all-style book suggesting everyone in Trump's entourage questions his mental stability.
The test that cleared Trump was developed by a doctor associated with McGill and Sherbrooke universities.