Could Rick Santorum pull off a surprise victory in this week's caucuses? Newt Gingrich thinks so.

"I think that Santorum's going to have a pretty good day tomorrow and he will have earned it. He targeted differently than I did," Gingrich told reporters gathered outside an energy forum in Golden, Colorado.

Gingrich credited Santorum's strategy of mostly skipping last Saturday's Nevada caucuses in favor of competing in Colorado and Minnesota. Both states hold caucuses on Tuesday.

Speaking to reporters after the same forum, Santorum opted against setting any expectations for the caucuses. But he questioned Mitt Romney's ability to close the deal with Republican voters, noting the former Massachusetts governor has failed to attract as many voters as he did in 2008 in some previous contests.

"He's underperformed from four years ago. And I suspect he will again," Santorum said about Tuesday's caucuses.

"The challenge for Romney is he's not expanding his world," Gingrich added at his separate media availability.

During a face-to-face meeting back stage at the energy forum, Gingrich and Santorum said they agreed Romney is not conservative enough to carry the Republican banner in the upcoming general election.

In a sign of Santorum's perceived strength in this week's caucus states, the Romney campaign spent much of Monday questioning the former Pennsylvania senator's spending record in Washington.

Santorum responded with a day-long barrage on the health care plan Romney signed into law in Massachusetts. Many Republicans see the program as the prototype for the president's health care law.

"Mitt Romney is uniquely positioned to give that position away," Santorum said to reporters.

Gingrich is looking beyond Minnesota and Colorado. He plans to spend Tuesday night in Ohio, a state that does not hold its primary until March. The former speaker noted early voting has already begun in Ohio.

Gingrich said he learned a major lesson in Florida: don't discount early voters.

"Forty percent of the vote was cast before the primary," Gingrich said.

The former speaker not only defended his plans on earth, but in space as well. He laughed off a skit on last weekend's Saturday Night Live that portrayed Gingrich as president of the moon, a dig at his proposal for a lunar colony.

"This is an American institution, they used to make fun of me all the time when I was speaker, and I took great pride in the fact that they made fun of me," Gingrich said of the SNL skit.

Gingrich told reporters he did ask Santorum to pull a radio ad that also pokes fun at the moon colony proposal, saying the spot falsely states the plan would cost a half-trillion dollars. The former speaker said he would first look for the money in the current NASA budget to pay for the proposal.

The former Pennsylvania senator said he is considering Gingrich's request to pull the ad.