U.S. Communists have been running for office for decades. Above, the Party's presidential ticket in 1936. Ken Rudin collection hide caption

itoggle caption Ken Rudin collection

Running mates? Mitt Romney greets former Gov. Mike Huckabee after taking part in a Republican presidential forum on Huckabee's Fox News program on Dec. 3, 2011. Henny Ray Abrams/AP hide caption

itoggle caption Henny Ray Abrams/AP

Rick Santorum holds his youngest child, Isabella, before announcing his run for the presidency on June 6 in Somerset, Pa. Santorum's campaign announced Friday that Isabella, who was born with trisomy 18, had returned to the hospital. Jeff Swensen/Getty Images hide caption

itoggle caption Jeff Swensen/Getty Images

The action was in Wisconsin Tuesday night, but Rick Santorum and his wife, Karen, had already moved on to his home state of Pennsylvania. They greeted supporters at an election night rally in Mars. Jason Cohn /Reuters /Landov hide caption

itoggle caption Jason Cohn /Reuters /Landov

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

Former House Speaker Newt Gingrich, who wants to the the 2012 Republican presidential nominee, during a campaign event in Camp Hill, Pa., on Saturday (March 24, 2012). Jessica Kourkounis/Getty Images hide caption

itoggle caption Jessica Kourkounis/Getty Images