Rick Santorum has won the Colorado caucuses, completing a superbly improbable sweep of the three states that voted Tuesday night.

When the last precincts reported around 1 a.m. EST on Wednesday, Santorum had 40.2 percent of the vote in Colorado to Mitt Romney's 34.9 percent. Newt Gingrich and Ron Paul trailed with 12.8 percent and 11.8 percent, respectively.

Recent polls had shown Santorum leading in Minnesota and Missouri, so those two wins did not come as a surprise. But his victory in Colorado was very much unexpected and a huge embarrassment for Romney, who took 60 percent of the vote there in 2008 and led the most recent pre-caucus poll by 10 percentage points.

The message of Tuesday's results was clear: Republicans are still searching for a conservative alternative to Romney, and Gingrich is no longer it.

That title is now Santorum's to lose. His task is to turn his three-state sweep into something durable -- and he will have to do so amid the toxic barrage of attack ads and stump-speech criticisms reserved for the front-runner du jour.

That is a formidable challenge (as Gingrich, Herman Cain and Rick Perry will readily attest), made especially so by Romney's seemingly bottomless pockets.

The main problem with Santorum and Gingrich and others is just their ability to fundraise on the level that Romney is able to, said Michael Berry, a political scientist at the University of Colorado at Denver (UCD). If they can stay afloat and continue to advertise and reach out to voters in states where these primaries or caucuses are continuing, I think it's possible they could still win the nomination, but [fundraising] is just so important in reaching out to voters in these states.

Given his financial advantage, the nomination is clearly Romney's to lose, in spite of Santorum's big night, Berry said.

UCD political scientist Michael Cummings added that Santorum still has a lot of work to do when it comes to broadening his base.

Santorum represents one of the five key factions of the GOP, namely the Christian right, Cummings said. The other four factions -- corporate, libertarian, law and order, and neoconservative -- have many conflicts with the Christian right, whose percentage of the GOP and of Americans has stagnated since 2000. Romney has a broader appeal to the other factions than Santorum.

Santorum, Cummings said, is an extreme long shot to beat Romney.

But that's tomorrow's discussion. Tonight, a campaign declared dead mere days ago is celebrating the unlikeliest of revivals.