In last week’s debate for the Republican presidential candidates, Rick Perry had an opportunity to backpedal on his criticism of Social Security, but instead, he doubled down. Among other things, the Texas governor called the program “a Ponzi scheme,” and said anyone talking about “ways to transition this program” is telling “a monstrous lie.”

For Mitt Romney and much of the Republican establishment, the comments couldn’t have been more important. The party, Romney and others said, simply can’t nominate someone this hostile to a popular American institution.

And with the next big debate on tap tonight, it seems very likely Social Security policy will take center stage. Going into the event, let’s take a look at how and why this matters to the two leading candidates.

Perry has an op-ed in USA Today this morning, and it looks like he’s already begun toning down his rhetoric. “For too long, politicians have been afraid to speak honestly about Social Security,” he writes. “We must have the guts to talk about its financial condition if we are to fix Social Security and make it financially viable for generations to come.”

This is clearly a departure from Perry’s record, which has suggested more than once that Social Security shouldn’t even exist. Now he wants to “fix” it? Yeah, sure he does.

Romney, meanwhile, is once again counting on public ignorance to advance his ambitions. To undermine Perry, Romney wants to position himself as a mainstream champion of Social Security, but there’s a lengthy public record that paints a very different picture.

[I]n 2007, when Romney was also campaigning for the Republican nomination for president, he supported his own radical change, repeatedly advocating for the privatization of Social Security, a plan pushed by Republicans and former President George W. Bush that failed in 2005.

At one debate, Romney was asked where he stood on privatization. Regarding Bush’s plan, Romney said, “That works.” […]

But Romney’s support of private accounts was hardly a one-time utterance at a single debate. Throughout that campaign, he touted the plan. […]

Romney did not abandon his support for privatization when his first presidential campaign ended. On page 160 of his book, No Apology, published in 2010, Romney again hinted at support for privatization.

Romney has spent a week arguing that Perry couldn’t possibly win a national general election because his approach to Social Security is too unpopular. But there’s the rub: Romney’s position on Social Security has been strongly and repeatedly rejected by the American mainstream, too.

Even the Weekly Standard, of all outlets, said last week, “[I]t’s hard to see how Romney’s hypocritical demagoguery is going to help him win the nomination. ”

This should make for some interesting fireworks in prime time tonight.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.