Jackson later was nominated by Trump to run the Department of Veteran Affairs, but the admiral withdrew his name after allegations of misconduct surfaced, including accusations he improperly dispensed medication.
"I would say, though, that despite that, one of the things, being with the president on a day to day basis, is that he has a lot of energy, a lot of energy and a lot of stamina", Jackson added.
President Trump is in great health according to the results of his latest physical exam.
Last year's examination revealed that President Trump has a common form of heart disease, as well as high cholesterol.
It remained unclear how numerous test results would eventually be made public.
"While the reports and recommendations are being finalised, I am happy to announce the President of the United States is in very good health and I anticipate will remain so for the duration of his Presidency and beyond", Sean P Conley, a Navy officer who is the president's physician and the current director of the White House medical unit, said in a statement.
Whatever the actual state of Trump's health is, that's quite the prediction.
The 45th president's diet, reportedly involving legendary amounts of Coke and red meat, also seems to defy most doctors' orders.
The doctor also declared that he had told the president he "might live to be 200 years old" if Trump would just eat healthier foods.
Trump did not undergo procedures that required anesthesia or sedation. More detail about the physical is likely to come next week.
"That speculation is both unnecessary and smacks of politically rosy glasses skewing age and weight and diet", said Arthur Caplan, an expert on medical ethics at New York University, said of Conley's prediction.
His doctor then said the president was in "excellent health" but would do well to drop 10 to 15 pounds and shift to a low-fat, low-carb diet and take up a more defined exercise routine. This can't be a coincidence.