Perhaps the most important part of last night’s Republican primary debate was the exchange between Rick Perry and Mitt Romney on the issue of Social Security. Perry stuck by his claim that Social Security is a ponzi scheme, and Romney responded with a strong electability argument against Perry: “Our nominee has to be someone who isn’t committed to abolishing Social Security.”

It was clearly an effort by Romney to make the case to Republican primary voters that he could beat Obama, whereas Perry would have some huge liabilities in the general election. Expect to hear this same basic argument repeated consistently by the Romney campaign throughout the primary. It is a message that Romney really needs the primary voters to hear.

Despite the fact that most major polls show Romney doing better in head-to-head match up against Obama, the Republican base currently doesn’t believe Perry is a general election liability. In fact the GOP base right now sees Perry as slightly more electable than Romney. In a recent ABC News/Washington Post poll among Republican and Republican-leaning independents, 30 percent said Perry stands the best chance of beating Obama, while only 20 percent said Romney does.

Romney doesn’t really inspire the GOP base, but the GOP base is enthusiastic about wanting Obama gone. Romney’s biggest potential advantage in the primary are the national polls which show that if the 2012 election is close,  he would be the GOP’s best (and possibly only) hope of beating Obama. But this is only a political advantage for Romney if he can make the primary voters believe it,  and so far they don’t. That is why Romney’s campaign is going to need to hammer in the electability message every chance they get.