He is going to be the Candidate, and no amount of money will be held back (nor has it been) in buying anti-ads in EVERY state he ran or will run in for the Primaries.
When he won Ohio; he had ads running continuously against Santorum, with lies, false statements, and out-of-context attacks....which worked for him, due to the ignorance of the bulk of the population, PLUS the backing of Big Business interests.
This is exactly why Santorum says FOX is pimping for Romney.