Do presidents have to have a physical while they are in office?
David M. Reiss, a California psychiatrist and a contributor to the book "The Dangerous Case of Donald Trump: 27 Psychiatrists and Mental Health Experts Assess a President" and a signatory on the letter, said Trump's pattern of behavior has been "disturbing and it's worrisome and it really needs attention". After Jackson last examined Obama, in February 2016, the memo he prepared included the president's height, weight, body mass index, resting heart rate, blood pressure, pulse oximetry and body temperature.
They can also include more detailed examinations of the heart, lungs, vision, cholesterol and blood glucose that could point to problems.
The president has pushed back against suggestions he's mentally unfit, declaring himself "a very stable genius". The White House wouldn't say whether doctors would test the president's cognitive abilities.
"Let Trump be Trump" was co-written by former Trump campaign manager Corey Lewandowski and claims dinner could be "two Big Macs, two Filet-O-Fish, and a chocolate malted (milkshake)". He uses a cart when plays golf. He doesn't smoke or drink alcohol. His diet is heavy on fast food, red meat and Diet Coke.
It's not clear how much information the president will share about Friday's work-up.
Jackson, the president's physician for three consecutive administrations, is scheduled to speak with reporters on Tuesday after compiling lab results over the holiday weekend - an unusual step in this annual White House ritual.