Newt is trying to deny Romney delegates. Nobody is going to beat Romney outright. The only chance is to deny him delegates. Period.
Since Santorum is the only other candidate who can be nominated, so far, he needs to win three states, or he should withdraw and plead with his supporters to support Santorum. At the moment, that is the only alternative to a Romney nomination.
Best bets:
Louisiana - currently 3rd
Wisconsin - distant 3rd
North Carolina - 3rd
Texas - 3rd
(recent polls)
He was leading in WV, NE, and MT, but that was back in November.
Arkansas, Kentucky, and South Dakota have no polls I can find.