Mitt Romney is pretty upset about Rick Santorum robo-calling Democrats to try and get them out to vote for him. Romney called it "a real effort to kidnap our primary process."

This might be why. In 2000, John McCain won Michigan by 8 points, 51%-43%, over George W. Bush. And about 10 percent of the people who voted for McCain were Democrats.

About 1.3 million voted in the 2000 Michigan primary. Nearly one-in-five -- 17% -- voters told exit pollsters they were Democrats. (That would be about 75,104 people; 82 percent of them went for McCain, meaning 61,586 Democrats voted for McCain.)

McCain's total vote was 650,805, so the 62,000 or so is about 9.5%. (Of course, these aren't exact numbers because exit polls have a margin of error but they're pretty close.)

Only about half -- 48% -- of the 2000 Michigan primary voters identified as Republicans; 35% were independents.