Tallahassee, Florida (CNN) Sen. Lindsey Graham, a 2016 candidate and close friend of Arizona Sen. John McCain, called businessman Donald Trump "a jackass" on CNN's "Erin Burnett OutFront" on Monday.

"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. "This is a line he's crossed, and this is the beginning of the end of Donald Trump ... I am really pissed."

On Saturday, Trump -- at a GOP political event in Iowa -- said McCain was "not a war hero."

"He is a war hero because he was captured," Trump added. "I like people that weren't captured, OK? I hate to tell you. He is a war hero because he was captured. OK, you can have -- I believe perhaps he is a war hero."

Bipartisan elected officials from the White House all the way to the wide open Republican primary field are using incendiary comments from Trump to praise former prisoner-of-war McCain

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