If Rick Santorum loses as handily in today’s Illinois primary as the polls predict, it will be interesting to see if he expands on his eye-opening new tack: going after Mitt Romney’s lucrative years at Bain Capital. Until this week, Santorum had stood out among Romney’s GOP challengers for refusing to hammer him on his business background, arguing that it was un-conservative for Newt Gingrich, Rick Perry and Jon Huntsman to take up that attack. I remember asking him in Somersworth, N.H., what he made of Romney’s comment that day that he “like[s] being able to fire people who provide services to me,” and having Santorum respond with a reluctant mumble. His reluctance to engage Romney on this front has been particularly striking given that Santorum is appealing to a downscale slice of the Republican electorate that would presumably be open to an anti-Bain message. In 2008, Santorum's social-conservative precursor, Mike Huckabee, gleefully went at Romney’s Bain background, saying that Romney “looks like the guy who fires you.” But not Santorum.

Until now, that is. In recent days, the Santorum campaign has clearly decided to rethink its abstemiousness on Bain. Yesterday morning, Santorum’s top strategist, John Brabender, challenged Romney’s business credentials by declaring (accurately) on MSNBC: “While Mitt Romney was at Bain Capital, almost one out of every four companies they were involved in either went bankrupt or out of business.” Later yesterday, Santorum followed up with this on the stump in Rockford, Illinois: “I heard Governor Romney here called me an economic lightweight because I wasn’t a Wall Street financier like he was. Do you think that’s the experience we need? Someone who’s going to take and look after, as he did, his friends on Wall Street and bail them out at the expense of Main Street America?’’

Keep an eye on this. Gingrich et al’s earlier attacks on Bain unquestionably softened up Romney for the Democratic attacks that will come on the same score in the months ahead (though I’ve argued that the attacks were far less influential with Republican primary voters in Newt’s brief flash of glory in South Carolina as others believe.) If Santorum now starts hammering hard on Bain as well, there’ll be quiet cheers in Chicago.