In an interview that aired Thursday morning on CBS, Graham was asked about the disconnect between his closeness with McCain and his efforts to work with the president.
“I am going to do everything I can to help President Trump, and when he's wrong, I will say so. ... It bothers me greatly when the president says things about John McCain. It pisses me off to no end, and I let the president know it,” he said.
Graham said he did not call Trump about lowering the White House flag back to half-staff this week but he did “call some people around him.”
After delivering an emotional tribute to his friend on the Senate floor earlier this, Graham told reporters the late Arizona senator offered him some advice on how to handle the president.
"He said, 'Help him where you can. Just don't get sucked into all his bull----,'" Graham said of his conversation with McCain.
Graham also told reporters it was "challenging" being close to both Trump and McCain because of their bitter feud.
The South Carolina Republican, himself a lawyer, was also asked in Thursday’s interview about a possible replacement for departing White House counsel Don McGahn.
“If I were the president, I'd pick somebody that understood the legislative branch,” Graham said. “Because if the Democrats take over the House, then he's going to be subpoenaed to death and investigated to death.”
On the topic of the special counsel investigation into Russia, Graham said he wasn’t convinced Trump has the ability to collude with any foreign government.
“I say this as a joke but it's kind of a half of a joke,” Graham said. “To collude, you got to sit down, come up with a plan and stick with it. Trump's not good at that.”