Sen. John McCainJohn McCainManchin bashes GOP candidate for pushing McCain to resign McCain’s primary challenger asks him to step aside after diagnosis Sen. McCain goes on hike after cancer diagnosis MORE (R-Ariz.) slammed Newt Gingrich on earmarks in a Wednesday afternoon conference call hosted by Mitt Romney’s campaign.

“Speaker Gingrich set into motion the largest explosion of earmarks in the history of Congress,” McCain said. “I was there, I saw the earmarks explode, I saw the corruption that it bred, and I saw the incredible waste of taxpayer dollars.”

McCain, long a foe of earmarks, endorsed Romney before New Hampshire’s primary. The attack line on Gingrich was the same one he used on Rick Santorum shortly after he endorsed Romney.

He also said there were two reasons why many House Republicans who served with Gingrich had come out for Romney in recent weeks. “One is because of his electability issue, which is substantiated by the polls,” McCain said. “Also, the fact is he was a failed Speaker: He could not have been reelected as Speaker of the House. His leadership style was a major factor.”

McCain also downplayed the importance of immigration in the GOP primary but warned that Republicans had to do a better job at reaching out to Hispanic voters.

“Quite honestly, the issue of the Hispanic vote is an issue for Republicans in the upcoming election and something we need to address,” he said, pointing out that he’d done poorly with Hispanics in 2008.

The Arizona senator beat Romney in the 2008 GOP presidential primary, and the two were known to have had a testy relationship on the campaign trail. 

They still disagree on campaign finance. Just days after McCain endorsed Romney, the former Massachusetts governor harshly criticized by name the McCain-Feingold campaign finance reforms.

McCain said he was “ashamed” of the Supreme Court’s ruling that allowed unlimited donations from people and corporations to outside groups, calling the super-PACs that have emerged “disgraceful.”

He said that there would likely be a “major scandal” to come from the super-PAC spending and blasted a super-PAC supporting Gingrich, arguing that a “casino owner” giving $10 million to help the candidate was not “what our Founding Fathers had in mind.”

But when asked about why he was backing Romney, who disagreed with him strongly on the issue, he said it was not the most important thing. “We’ve never agreed on every issue. I think the important issues right now are jobs, the economy and national security,” McCain said.

“I’m pleased to support him,” he said, adding that he looked forward to discussing campaign finance reform further with Romney.