Even if Mitt Romney has a relatively good night tonight, Rick Santorum could still expose a weakness in the former Massachusetts governor’s candidacy: Romney has lagged behind in winning the votes of blue-collar conservatives and working class Americans. These voters will be very important in the general election, as Barack Obama has had very little rapport with them dating all the way back to his 2008 primary campaign against Hillary Clinton.

That’s why Santorum is making a late-minute stop in Cuyahoga County today. Granted, the argument will be blunted somewhat if Romney follows up his narrow win in Michigan with another squeaker in Ohio. But the breakdown of the electorate will matter a great deal. Romney is going to need to put together a broad center-right coalition of voters if he is the nominee. Santorum will press the case that despite his harder-edged conservatism, he is the one better equipped do to do so — if the data supports that argument.