“It bothers me greatly when the president says things about John McCain,” said Graham, a longtime friend and colleague of McCain. “It pisses me off to no end. And the way he handled the passing of John is just—it was disturbing.”

McCain, a harsh critic of Trump, died of brain cancer Saturday after more than 30 years as a U.S. lawmaker. Despite his service as both a senator and a Vietnam war veteran, Trump hesitated to release an official statement acknowledging McCain’s contributions to the country. He instead tweeted a short message offering his “deepest sympathies and respect” to the McCain family.

The president’s controversial decisions continued Monday: after remaining at half-staff for most of the weekend, the White House flag was raised to full-staff, defying tradition that government flags remain lowered until the burial of a prominent politician. Trump ordered the flag back to half-staff later on Monday, after facing harsh criticism.

On CBS, Graham said that while he hadn’t called the president directly, he called “some people around him” to ask that the flag be lowered.

Despite their differences on how to manage Trump’s often erratic policies, Graham said he will honor his friend by continuing to work with the president.

“I am not going to give up on the idea of working with this president,” said Graham. “The best way I can honor John McCain is to help my country.”

Still, Graham said he will be straightforward with Trump, especially on the issue of special counsel Robert Mueller’s probe, which Trump has long derided as a “witch hunt.”

“Here’s what I’ll tell the president: there is no scenario where you can end this investigation—the Mueller investigation—through some political intrigue, and survive,” said Graham. “That’s the end of you. The only person in America that can clear Donald Trump is Mueller.”