MI PrimR: Public Policy Polling: Santorum leads by four

[ajb]

My hunch is that a week ago Santorum supporters were highly motivated to vote (because they saw their guy had a chance to win), while Romney supporters were less motivated, partly because they're just less passionate about their guy, partly because they were complacent. A certain number of Republican voters may now be more energized to vote Romney to stop Santorum (even as there's another large block doing the opposite).