Conventional wisdom says that Mitt Romney is a more viable candidate than Rick Santorum in a head-to-head fight with President Obama. Polling bolsters that viewpoint, though by a slight margin. But my sense is that the so-called Romney-Santorum electability divide underestimates one of Romney’s biggest liabilities in the general election: His aura of being the guy who just fired you.

Now, free marketeers in the Republican base understand Romney’s tenure at Bain Capital. They don’t have a problem with his net worth. Swing voters won’t have nearly as sanguine a view, especially as they’re fed misinformation by Obama’s $1-billion campaign machine. A well-orchestrated attack by Obama against Romney’s background and wealth could be just as effective — if not more so — than an attack leveled against Santorum’s social conservatism. That’s especially true if Romney continues to let slip such utterances as “I like being able to fire people who provide services to me,” “I’m not concerned about the very poor,” and “corporations are people, my friends.”

Of particular concern to Republicans should be Romney’s precipitous slide in the polls among independents. It’s not because the former Massachusetts governor is emphasizing his social conservatism more. It’s because swing voters don’t trust or like him, even though they’re fed up with Obama and the poor economy. As Nate Silver of The New York Times has written, the electability divide between Romney and Santorum isn’t as significant as one might think. Also check out results from the left-of-center Public Policy Polling finding that Romney’s electability argument is weakening. (A caveat: Some of Santorum’s positive polling could be because his “dirty laundry” isn’t yet as visible as Romney’s.)

No doubt, Santorum’s social conservatism would be a liability with swing voters. But so would Romney’s background and perceived lack of trustworthiness. As Jim has pointed out, Santorum’s more pressing problem would be assembling a presidential campaign on the fly, not his social conservatism.

Another aspect that’s underestimated: Santorum would excite evangelical (and perhaps Catholic) voters in a way that Romney never could. Although libertarians have criticized Santorum’s track record on fiscal concerns, his sins are far less numerous than Romney’s. So it’s quite possible that a strong Santorum campaign could generate a more energized Tea Party voting base. Yes, swing voters are critical, but so is turning out the base. Santorum would give conservatives a candidate to vote for rather than merely an incumbent to vote against.