BOISE, Idaho (AP) -- Rick Santorum is the latest Republican to surge in presidential preference polls. Now he's trying to turn his newfound strength into something lasting.
Curious Republicans pack his rallies. Supporters have funneled nearly $4 million to his formerly empty campaign account over the past seven days. And Santorum's staff is plotting an aggressive strategy to challenge Mitt Romney in Romney's native Michigan and beyond.
But there is weakness just beneath the surface.
Santorum is underfunded and out-manned. It's unclear if he can protect the standing he's gained in polls. And now his opponents -- on the right and the left -- have begun to implement their own strategies to tear him down.