Rick Santorum is wiping the sweat from his forehead. That's okay. Everyone Sweats. But didn't Momma tell you never to let 'em see you sweat? It's not necessary to tilt your head down to wipe one's forehead - but Santorum and most everyone does this when anxiety is a contributing factor. Self-touching (although here there is a handkerchief "insulating" - for the most part - against a direct touch) fits into a class of nonverbal behaviors known as Manipulators, Adaptors or Pacifiers (MAPs). There are certainly some exceptions, however the vast majority of MAPs indicate anxiety. Often there is another coexisting negative emotion being expressed as well. Rick has a mild amount of mid-face tightening along with subtle nasal flaring. We cannot see the right side of his face - and thus this could be a subtle display of contempt - if unilaterally expressed. If both sides of the former U.S. Senator's face looks like this - then this body language is a mild display of disgust.
Tonight was a huge disappointment to Rick Santorum, as Mitt Romney won both the Michigan and Arizona Primaries. Chin up Rick. There's always Super Tuesday.