The pro-Mitt Romney super PAC, Restore our Future, burned through $4 million in just three days this week on independent expenditures in half a dozen states with upcoming primaries. If it keeps up this rate, the super PAC would spend more than $16 million in the 12 days leading up to Super Tuesday, topping the total it spent in January.

Six states with primaries in the next two weeks--Arizona, Georgia, Ohio, Oklahoma, Michigan, and Tennessee--all saw a spending spike.

In Michigan, where voters go to the polls next week, the super PAC supporting Romney pummeled opponent Rick Santorum with more ...