According to South Carolina Sen. Lindsey Graham, businessman Donald Trump is a "jackass."

The comments come after Trump — who like Graham is running for the 2016 Republican presidential nomination — said over the weekend that Arizona Sen. John McCain is "not a war hero" because he was captured.

Graham and McCain are known to be close friends.

"What he said about John, I think, was offensive. He's becoming a jackass at a time when we need to have a serious debate about the future of the party and the country," Graham told CNN's Kate Bolduan Monday night. "This is a line he's crossed, and this is the beginning of the end of Donald Trump ... I am really pissed."

Graham said Trump's comments are not welcomed in the Republican Party, which is "the party of the military."

Graham also criticized the media for focusing just on Trump while "the world is literally falling apart."

On Monday night in an interview with Fox News' Bill O'Reilly, Trump half apologized to McCain after standing by his comments earlier in the day on NBC.

"I used to like him a lot. I supported him. I raised a lot of money for his campaign against President Obama, and certainly, if there was a misunderstanding, I would totally take that back," Trump said after claiming his respect for McCain. "But hopefully, I said it correctly and certainly, shortly thereafter, I said it correctly."

Early Monday morning, McCain said Trump owed all veterans and prisoners of war — not just himself — an apology.