Jimmy Kimmel on Thursday revealed his theory on why Republicans don’t want President Donald Trump testifying under oath about his relationship with late convicted sex offender Jeffrey Epstein, who was once a close friend.

The president’s name is in the files so often that Kimmel is calling on people to refer to them as the “Trump-Epstein files.”

Yet while other prominent figures ― including former President Bill Clinton and former Secretary of State Hillary Clinton ― have testified, and Attorney General Pam Bondi has just been subpoenaed, Trump has not.

Kimmel has a theory on that.

“If you’re wondering why Bill Clinton, Hillary Clinton, and now Pam Bondi have to testify and Trump doesn’t, it’s because you can’t put Donald Trump under oath,” Kimmel said. “If he swears to tell the truth, that’s already perjury.”

See more in his Thursday night monologue: