Sen. John McCain (R-Ariz.), right, and GOP presidential candidate Mitt Romney. (Charles Dharapak/Associated Press)

“All I can say is that I was there,” McCain told reporters on a conference call Wednesday afternoon, “I saw the earmarks explode. I saw the corruption that it bred, and I saw the incredible waste of taxpayers’ dollars, not just on the famous Bridge to Nowhere but earmark after earmark after earmark, which were in the thousands.”

The call was the latest in a Romney camp offensive by current and former members of Congress slamming Gingrich’s tenure in the House. It also comes as Gingrich is ramping up his attacks on Romney, particularly on the issue of immigration.

McCain, a 2008 rival of Romney’s who endorsed the former Massachusetts governor ahead of this year’s Jan. 10 New Hampshire primary, charged that during Gingrich’s “failed” speakership, “the number of earmarks doubled to more than 6,000 projects in the range of billions of dollars. So, I don’t think that with a $15 trillion debt that we can afford to have that.”

While it’s true that congressional earmarks were commonplace during Gingrich’s tenure in the House, the legislative pet projects persisted for years after Gingrich. It has only been in recent years that members – fueled in part by voters’ renewed focus on the national debt — have revolted against the earmarking process.

The surge at the time of Gingrich’s speakership was fueled in part by a political strategy, spearheaded by Gingrich, to help vulnerable Republicans keep their seats in the House. The period marked a crucial turning point in the use of earmarks, which until then had primarily been the province of a handful of powerful committee chairmen.

Even then, it’s also worth noting that at 1 percent of the federal budget, earmarks typically comprise only a small sliver of annual government spending.

McCain on Wednesday also took aim at Gingrich’s work for Freddie Mac, which paid the former speaker $1.6 million. Gingrich has defended his work for the mortgage giant, contending that he worked as a “historian” and not a lobbyist.

“I don’t think that historians are well-enough paid, but I’m impressed that a historian would be paid by Freddie Mac some $25,000 a month, totaling about $1.6 million,” McCain said Wednesday. “Obviously, I am a strong supporter of Mitt Romney. ... I believe that we will clearly see a difference between the kind of outlook that is practiced by Newt Gingrich and Mitt as governor of the state of Massachusetts.”