Wisconsin will hold its Republican presidential primary on April 3. From Rasmussen Reports (Released 3/23):

A new statewide telephone survey shows that 46% of Likely Republican Primary Voters in Wisconsin favor Romney, while 33% prefer Santorum. Texas Congressman Ron Paul is a distant third with eight percent (8%) of the vote, closely followed by former House Speaker Newt Gingrich at seven percent (7%). One percent (1%) favors some other candidate, and five percent (5%) are undecided. 

This Wisconsin survey of 1,000 Likely Republican Primary Voters was conducted on March 21, 2012 by Rasmussen Reports. The margin of sampling error is +/- 3 percentage points with a 95% level of confidence.