This chart from Gallup is probably making people in the Santorum campaign panic, at least a little. Santorum's popularity is in dark green, Romney's is black (matches his soul), Newt's is orange and Ron Paul's is light green:
If these were stock charts, I would say that it would make sense to lighten up on Romney as there is a lot of resistance at 36%, that Santorum still has a ways to go down (probably to 18%) and that Newt could be a buy as he has formed a base and seems to be trending up a little. Ron Paul looks like a value trap. A stock that you can make a good fundamental argument why it should go up but never goes anywhere.