Supporters listen to Republican presidential candidate Rick Santorum at The Ravine in Bellevue, Wis., on March 24. Some voters in the state are complaining about a barrage of negative ads in advance of Tuesday's primary. Darren Hauck /Reuters /Landov hide caption

itoggle caption Darren Hauck /Reuters /Landov

Volunteers at the Wisconsin Democratic Party's recall office in Waukesha entered names from petitions to recall Gov. Scott Walker into their voter databases on March 20. Liz Halloran/NPR hide caption

itoggle caption Liz Halloran/NPR