"I think he crossed a line with a lot of people, not just me. John is my best friend in politics and one of my best friends in life," Graham told The Huffington Post at a campaign stop in Iowa on Saturday. "This will work out. Iowa, New Hampshire, South Carolina Republicans are conservative, but they aren't going to put up with this. This will work itself out. I'm not calling for him to get out of the race, I'm calling for people of Iowa, New Hampshire, South Carolina to tell him he's fired."
"If you want to be commander in chief, you need to understand how the military works. Being captured doesn't mean you're a loser, it means you put yourself at great risk and you probably are young to go through hell while you're in captivity. It just shows a lack of understanding of the military, lack of respect for those who have served," he added.
McCain spent five and a half years in a North Vietnam prison where he was tortured after his bomber plane was shot down in 1967. Trump has refused to apologize for his remarks, despite near unanimous denouncements from his Republican rivals for the White House.
Graham said Trump's latest antics were the last straw.
"I can understand being frustrated about immigration, but there's no justification to slander a bunch of people that are hardworking folks," he said. "This is a line that is crossed. I think the American people, the caucusgoers, the primary voters are going to fix this. To the other candidates, this is your chance to do the right thing and disassociate yourself from somebody who has basically shown a lack of judgment to be commander in chief and to be president of us all."