President Trump voluntarily took the test as part of his annual physical examination because certain media were insinuating that he was not mentally fit.
Then he didn't to Trump any favors. Trump seems to think he took some kind of IQ test, that the test was "very hard", and that he aced it and he brags about it. The test in question should not be hard at all for anyone with normal cognitive skills. The only reason for giving it in the first place if you think the person being tested is losing their memory or having problems thinking. If asked about his mental fitness Jackson should just have said that the physical and his observation of Trump on a daily basis have shown no indication that Trump's cognitive skills were declining and left it at that.