Lindsey Graham says everyone running for president, including Trump, should take cognitive tests to prove they're fit for the top job

Justin Sullivan, Kevin Dietsch, Andrew Harnik/Getty Images

• Sen. Lindsey Graham says he thinks presidential candidates should all take cognitive tests. 
• Biden and Trump should both have to prove their fitness to run for office, he said to CBS. 
• His comments come as Biden faces mounting pressure to quit the race over health concerns.

Sen. Lindsay Graham says he thinks anyone running for president should undergo a cognitive test — including his longtime ally, former President Donald Trump.