Donald Trump will have his first medical exam as U.S. president today, after a week during which his mental fitness for the job has come under intense scrutiny.

A new bestselling book, Michael Wolff's Fire And Fury, portrays Trump, 71, as unfocused and childlike. The White House has faced a barrage of questions over his contradictory messages on key policies and an incident last month where he slurred some words while giving a speech.

Trump, who has been openly exasperated with the coverage, told reporters on Thursday he expected his exam would go well.

Michael Wolff's book Fire And Fury portrays Trump, 71, as unfocused and childlike. Questions have been raised about Trump's mental fitness. (Phil Noble/Reuters)

"It better go well, otherwise the stock market will not be happy," Trump said with a smile.

The White House will determine what data will be released from the exam, which will take place at the Walter Reed National Military Medical Center in nearby Bethesda, Md.

Trump is not compelled to release any information, though the White House said the presidential physician, Ronny Jackson, will provide a statement on Friday and take questions from reporters on Tuesday.

No psychiatric exam

There is no set template for the presidential exam. 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 was diagnosed with Alzheimer's disease.

Trump's examination will not include a psychiatric exam, a White House spokesperson said this week. Results of past presidential physicals have included basic data like weight, blood pressure and cholesterol levels.

There is a long history of the White House picking and choosing what to reveal about the commander in chief's health, said Barbara Perry, director of presidential studies at the University of Virginia's Miller Center.

For example, John F. Kennedy disclosed war injuries but not the fact that he suffered from Addison's disease, a degenerative condition.

Perry said she believes presidents should be subjected to a raft of tests to establish they are fit to serve.

When he was running for office, Trump released a glowing letter from his personal physician in New York, who said Trump would be "the healthiest individual ever elected to the presidency."

What we know

The letter put Trump's blood pressure and cholesterol measurements in the healthy range, though Trump uses a cholesterol-lowering statin medication. His EKG, chest X-ray, echocardiogram and blood sugar were normal. The 6-foot-3 Trump weighed 236 pounds, and his body mass index, or BMI, of 29.5 put him in the category of being overweight for his height.

Trump takes Crestor for his cholesterol, a low-dose Aspirin for heart attack prevention, Propecia to treat male-pattern baldness and antibiotics for rosacea. The doctor's 2016 letter said Trump's testosterone level, 441.6, was in the normal range, as were his PSA reading for prostate abnormalities and tests of his liver and thyroid.

The public report from Trump's exam on Friday is also likely to be short and sweet, said George Annas, head of the Center for Health Law, Ethics and Human Rights at Boston University School of Public Health.

"I don't think you could expect to see anything else, unless it's something that makes him look good," Annas said.

Trump was 70 when he took office on Jan. 20, 2017, making him the oldest person ever sworn into the nation's highest office.