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

• Sen. Lindsey Graham said he thinks all presidential candidates should take cognitive tests.
• Joe Biden and Donald Trump should both have to prove their fitness to run for office, he told CBS.

Sen. Lindsey Graham said Sunday that he thinks anyone running for president should undergo a cognitive test — including his longtime ally former President Donald Trump.

Speaking on CBS's "Face the Nation," the South Carolina Republican said that given "70% of the public believes that President Biden is not mentally and physically capable of being president," he should take a cognitive test to prove his mental capabilities.

The CBS host Robert Costa then asked whether Graham thought Trump should have to take the test as well.

"Yes, yes, I think both," Graham said. "All nominees for president going into the future should have neurological exams as part of an overall physical exam."

He added: "Here's what I worry about, that our allies see a compromised Joe Biden, that our enemies see a compromised Joe Biden, and I'm offended by the idea that he shouldn't take a competency test given all the evidence in front of us."

Trump challenged President Joe Biden to take a test before the CNN presidential debate that saw the latter delivering an abysmal performance.

Speaking at a Turning Point Action convention in Detroit on June 15, Trump said: "He doesn't even know what the word 'inflation' means. I think he should take a cognitive test like I did."

The former president said he took a cognitive test in 2018 and has since bragged about it, saying he "aced" it "very hard."

However, the test's creator said the assessment was "not meant to measure IQ or intellectual skill in any way" but to detect whether someone has cognitive problems like memory issues.

Any adult without cognitive issues should get a high score, per the creators of the test. And Trump has not taken the test again after 2018.

Graham's comments came as Biden grappled with intense backlash after his bad debate performance on June 27.

Several of Biden's supporters have called for him to leave the race.

Five House Democrats have called on Biden to quit, predicting that he would lose to Trump in the November presidential election.

However, Biden has stayed resolute despite the mounting pressures. In an interview with ABC News on Friday, he called his mumbling and incoherent sentences during the debate a "bad episode" and "no indication of any serious condition."

Since the debate, his campaign has offered a series of reasons to explain his less-than-stellar performance, including a cold, jet lag, and bad prep.

Representatives for Biden, Trump, and Graham didn't immediately respond to requests for comment sent outside regular business hours.