Sen. John McCain (R-AZ) has seen some dirty campaigns in career, but on Sunday he said the 2012 Republican primary was "nastiest" one ever.

During the 2000 Republican presidential primary, then-Texas Gov. George W. Bush's top strategist, Karl Rove, put forward the idea that McCain had "fathered an illegitimate black child." As The Nation noted, McCain had been campaigning with his dark-skinned daughter who he had adopted from Bangladesh. The dirty trick gave Bush the boost he needed to win South Carolina.

During a Sunday interview on NBC, the Arizona senator said that unlimited money from super PACs have made the 2012 primary campaign even worse.

"Super PACs have played a key role, unfortunately in my view," McCain told NBC's David Gregory. "Most of them run negative ads. They've driven the unfavorables of all the candidates and made it much more difficult, frankly, to win the election in November."

"This is the nastiest I have ever seen," he added. "It's a result the of the worst decision the United States Supreme Court has made in many years, the Citizens United decision, where out of naivety and sheer ignorance, the Supreme Court just released all money [into the political process]."

Watch this video from NBC's Meet the Press, uploaded March 18, 2012.