Trump says Biden should take cognitive test -- because US requires 'sharp' leader

President Trump joins Fox News medical contributor Dr. Marc Siegel for an exclusive interview on'Tucker Carlson Tonight.' Joe Biden should take the same cognitive test that President Trump recently took, the president said Wednesday during an interview with Fox News medical contributor Dr. Marc Siegel. "In a way he has an obligation to," Trump said of the presumptive Democratic presidential nominee, adding that the presidency requires "stamina" and "mental health." Trump said he took the test to prove to the media that he was fit to serve in the presidency after reports supposedly questioned his cognitive ability. Trump has used the argument that Biden -- at age 77, three years older than Trump -- is too old to run for president . The argument is a cornerstone strategy of Trump's reelection campaign against the former vice president.