The Santorum campaign, anticipating a wave of negative attacks from the Romney campaign and super PAC, releases a new ad the features a Romney clone shooting mud at a cardboard cutout of Santorum:
https://youtube.com/watch?v=OtOcrS6axnE
However, the most recent numbers, per ABC News, show that Santorum is being badly outspent in Michigan: his campaign has bought $41,000 worth of airtime in the state, while the Romney campaign has purchased $824,000.