Republican presidential candidate Rick Santorum stumps in Boise, Idaho, at Capital High School on Tuesday. [Katherine Jones / Associated Press]

BOISE, Idaho - The latest Republican presidential contender to surge in the polls, Rick Santorum is trying to turn his newfound strength into something lasting that will establish him as the conservative challenger to Mitt Romney. But things don't look so strong for the former Pennsylvania senator just beneath the surface.

Three new polls show Santorum, coming off a stunning sweep of three state contests last week, has pulled even with presumed front-runner Romney in the race to challenge President Barack Obama in the November election.

The shift in the polls for Santorum continues the startling swings in a contest that has been notable for its instability. It also comes during a lull in state-by-state voting and in the debates that have kept candidates in the public eye.

Republican voters have been unable to coalesce around one candidate as both the most electable against Obama and sufficiently conservative to win strong backing from the tea party and evangelical Christian base voters. Santorum claims he is the leading conservative in the race, while Romney has been pitching himself to conservative voters who have doubts about his former, more moderate, positions on key social issues such as abortion.

A saving grace, perhaps, for Romney is that his level of support in the polls has held roughly steady while a series of challengers, Santorum being the most recent, have enjoyed a tie with or lead over the former Massachusetts governor.

Curious Republicans now pack Santorum's rallies. Supporters have funneled nearly $4 million to his formerly empty campaign account over the past seven days. And his staff is plotting an aggressive strategy to challenge Romney in Romney's native Michigan and beyond.

But Santorum is underfunded and outmanned. He's still lacking in organization, a month and a half into the primary season. And, after he won three contests in a single day last week, his opponents - on the right and the left - have begun their own efforts to tear him down.

An upbeat Santorum faced more than 1,000 people in a Boise, Idaho, high school auditorium on Tuesday night and said his ideas would carry him through.

He said he's someone "who can overcome the disadvantages of money and media attention and still be in a position to win. Ideas matter".

But his challenges were on display the day before in Tacoma, Washington state, where hundreds of supporters waited on cold, wet cement stairs in the dark to see the Republican presidential candidate with whom they're barely familiar and he was heckled by liberal protesters from a nearby Occupy encampment.

Santorum has surged to a virtual tie with Romney in nationwide polling following his surprising sweep in Colorado, Minnesota and Missouri last week. But his popularity may have less to do with who he is than who he isn't. Santorum is not Romney. And with Newt Gingrich's recent decline, that's enough for some conservatives - at least for now.

A New York Times/CBS News poll released on Tuesday showed Santorum with 30 percent support among Republican voters, three points ahead of Romney but within the survey's margin of error.

The new poll essentially mirrors results in surveys by the Pew Research Center for the People & the Press and the Gallup organization.

The Pew results released on Monday showed Santorum two points up with 30 percent support. Gallup showed Romney maintaining a two-point lead with 32 percent support. Both results were within the surveys' margins of error.

Both Pew and Gallup showed Santorum shooting up 14 points from a month ago.

Romney and others are now working to raise questions about Santorum's record as a lawmaker.

Associated Press