Sen. John McCain isn't happy about the drawn-out Republican nomination process.

McCain visited the Tonight Show last night to complain that the GOP candidates were tearing each other to pieces. He said a lot of the blame lies on the Supreme Court's Citizens United decision striking down campaign-finance limits and that the justices "should be ashamed and embarrassed by what they did."

On primary night, McCain told the Boston Herald:

“This is like watching a Greek tragedy,” McCain told the Herald. “It’s the negative campaigning and the increasingly personal attacks ... it should have stopped long ago. Any utility from the debates has been exhausted, and now it’s just exchanging cheap shots and personal shots followed by super PAC attacks.”

The Arizona Republican, who endorsed Romney earlier this year and is set to rally with him in Phoenix tonight, said he believes the former Bay State governor will get the nomination, yet he worries a long, drawn out primary campaign could leave Romney too wounded to triumph in November.

“I know he’s going to be the nominee but I also worry about how much damage has been done,” McCain said. “I think we still can win. ... Once we get this over, the more we’ll be focused on Obama’s failures.”