"This is like watching a Greek tragedy," McCain told the Boston 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 senator endorsed former Massachusetts Gov. Mitt Romney this year and was to rally with him in Phoenix Tuesday night as results from Arizona's and Michigan's primaries arrive.
McCain said he believes Romney will win the nomination but expressed concern he could be hurt so badly in the Republican primary battle royale he couldn't win in the general election against the Democratic incumbent in November.
"I know [Romney is] 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."
McCain's comments came Monday, the day a bipartisan Politico/George Washington University poll showed Obama's job approval had climbed to 53 percent and all four Republican candidates lagged by double figures in potential match-ups with the president. Obama led Romney by 10 percentage points in the poll.