Romney shrugged off his poor showing, but his losses Tuesday in Missouri, Minnesota and Colorado laid bare his stubborn weakness just when it looked as if his party was beginning to embrace him. Bringing up the rear of the Santorum surge: Newt Gingrich, the former House speaker who mostly skipped the contests and finished at or near the back of the pack in all three states.
Santorum cast the results as a victory for a purer form of conservatism than Romney has offered, heard more clearly by voters across the nation's midsection without a deafening TV air war that the former Massachusetts governor has dominated.
The former Pennsylvania senator said in a nationally broadcast interview Wednesday morning he thinks conservative Republicans "are beginning to get" that he represents the party's best chance to oust President Barack Obama.
He also used the opportunity to rip into Romney, mocking his criticism of Santorum's time in Washington in the U.S. Senate and Romney's attempt to be seen as the political outsider in 2012.
Santorum scoffed at Romney's criticism of his defeat for re-election to the Senate, saying, "A lot of folks lose races, but I didn't lose, like Gov. Romney, my principles. I wasn't a well-oiled weather vane."
He said he wants to make Obama "the issue in this race," not Romney and Gingrich.
Of Obama, Santorum said: "He believes he's the smartest guy in the country and he should tell people what to believe and how to live their lives."
Santorum also said, ""Mitt Romney is saying I'm not a conservative. I mean, that's laughable."
In the glow of victory Tuesday night, he told his supporters "we had an opportunity to see what a campaign looks like when one candidate isn't outspent 5- or 10-to-1 by negative ads impugning their integrity and distorting their record. This is a more accurate representation, frankly, of what the fall race will look like," a jubilant Santorum told a cheering crowd in St. Charles, Mo.
But it was far from clear that Santorum, who has a post office box for a campaign headquarters and relies on volunteers to handle scheduling, can quickly turn the momentum into the millions of campaign dollars he would need to overcome Romney. Still, he looked past the nomination fight.
"I don't stand here to be the conservative alternative to Mitt Romney, I stand here to be the conservative alternative to Barack Obama," Santorum said. On health care, cap and trade and the Wall Street bailout, he charged, "Mitt Romney has the same positions as Barack Obama."
In Denver, Romney congratulated his rival. The revived questions about Romney's appeal with conservatives at the party's core were even sharper in light of his aggressive push to court them in recent days. Santorum's shoestring candidacy thrived. And the GOP nomination fight many in the party hoped would resolve itself after Super Tuesday now threatened to rumble past March 6 - while Obama watches from his presidential perch in the White House, and waits.
"This was a good night for Rick Santorum," Romney told supporters in Denver on Tuesday night. He offered a bit of forced optimism: "We'll keep on campaigning down the road, but I expect to become our nominee with your help."
Romney added, "When this primary season is over, we're going to stand united as a party behind our nominee to defeat Barack Obama."
He wasn't the only loser.
On the first day of multi-state voting, the trio of contests exposed a glaring deficiency for Gingrich.
The former House speaker lacked the resources and organization to compete just as he's trying to project strength heading into the Super Tuesday elections. He made only minimal efforts in the three states that voted and stayed out of sight as the results rolled in. Gingrich is focusing on Ohio, where early voting has begun in the March 6 primary.
Texas congressman Ron Paul, meanwhile, reveled in his second-place win in Minnesota and vowed to keep collecting delegates to take to the GOP's national convention this summer.
To be fair, Tuesday's contests will have little bearing on the race for delegates. Missouri's nonbinding primary in particular was little more than an extensive warm-up routine. The state will hold an official caucus in March.
But even symbolic victories can produce or slow down momentum.
Romney's camp began downplaying the results hours before the voting began. Rich Beeson, his political director, released a memo earlier in the day noting that even Sen. John McCain lost 19 states on the way to capturing the GOP presidential nomination in 2008. And Missouri Sen. Roy Blunt, the director of Romney's congressional endorsements, released a statement as the votes began showing his candidate had lost in Blunt's home state.
"I congratulate my friend Rick Santorum on his win tonight," Blunt said. "But the fact remains that this is a nonbinding primary, meaning Missouri's delegates are still very much up for grabs."
Following Maine's low-profile caucuses, which conclude Saturday, the candidates will have an extended lull. Beeson recently noted that momentum would be vital heading into the 17-day period without an election, something he likened to a grand canyon with no precedent in modern presidential politics.
"If you don't have momentum and resources coming into it, it's going to be hard to have momentum and resources coming out of it," Beeson said.
That was a week before he realized his boss would suddenly see his momentum disappear.
Santorum was interviewed Wednesday morning on CNN, Fox News Channel's "Fox & Friends" and MSNBC.