BOW, N.H. — While Donald Trump called for a do-over, Marco Rubio tried to capitalize on his moment in the spotlight as the shrinking field of Republican presidential hopefuls jockeyed for position in a race rattled by surprises Wednesday.

Trump took to Twitter to vent his frustration with the Iowa results that landed him in second place and gave fresh hope to Republicans eager for a Trump-less race.

Among those is Florida Sen. Rubio, who seized on his third-place finish to cast himself as the sole “unifier” in a fractured party and the man best positioned to beat a Democrat in November.

Kentucky Sen. Rand Paul and former Pennsylvania Sen. Rick Santorum dropped out of the race Wednesday, putting their bloc of supporters up for grabs for the other contenders.

Paul had tried to improve the GOP's popularity among younger voters and minorities. But his appeal never broadened much beyond the small group of libertarian-leaning Republicans who backed the previous White House bids of his father, former Rep. Ron Paul of Texas.

Santorum, the deeply conservative former senator who won 11 contests in the 2012 race for the GOP nomination, ended his bid for the White House and backed Rubio.

Santorum said Wednesday night on Fox News Channel that Rubio is a “born leader” and praised his “optimistic” message.

“When I am our nominee, I can bring this party together,” Rubio told more than 300 people at an athletic complex in Bow. “We cannot win if we are divided against each other.”

For Ohio Gov. John Kasich, New Jersey Gov. Chris Christie and former Florida Gov. Jeb Bush, New Hampshire increasingly looked like a do-or-die proposition: Show some momentum or pack it up.

They hustled across the state trying to prevent the GOP presidential race from becoming a three-man contest.

Trump was far away in Arkansas but still getting plenty of attention.

Gone was the humble candidate who conceded to Texas Sen. Ted Cruz on camera Monday night. In his place was a take-no-prisoners Twitter rant.

“Based on the fraud committed by Senator Ted Cruz during the Iowa Caucus, either a new election should take place or Cruz results nullified,” Trump tweeted, following up on an earlier tweet claiming that “Ted Cruz didn't win Iowa, he stole it.”

On Tuesday night in New Hampshire, Trump told reporters he was “very happy with what happened in Iowa.”

But by Wednesday, Trump was laying out a list of accusations.

He pointed to a mailer sent by the Cruz campaign headlined “voting violation” that resembled an official notice. The mailer showed recipients their caucus voting histories, along with the turnout records of their neighbors, and drew complaints from Iowa's secretary of state.

Trump also called out Cruz backers for circulating a rumor Monday night that Ben Carson was dropping out of the race as caucusing was underway.

“Many people voted for Cruz over Carson because of this Cruz fraud,” Trump wrote, suggesting the efforts may have given Cruz a winning edge.

Iowa Rep. Steve King, a national co-chairman of Cruz's campaign, wrote on Twitter on Monday evening: “Looks like (Carson) is out. … Skipping NH & SC is the equivalent of suspending. Too bad this information won't get to all caucus goers.” Carson has called the comments “dirty tricks.”

Cruz spokesman Rick Tyler told CNN on Wednesday that Cruz apologized to Carson for the mistake. He said the Cruz team “as a campaign” never alleged Carson was dropping out.

“It may be that some of the surrogates or some of our caucus precinct captains … went too far,” Tyler told CNN. If so, he added, “that was in error, that was wrong.”

Cruz said Trump simply can't stand to lose.

“Donald Trump guaranteed a victory in Iowa and then he lost,” Cruz said. “And he doesn't like that. And his reaction is that he breaks down. He really has problems.”

For his part, Carson spoke of “deceptive Iowa caucus tactics,” implying that he, too, was upset about the false claim.

“It's clear that there were people who tried to take advantage of a situation,” Carson said.

Trump campaign manager Corey Lewandowski was pointed on the matter Wednesday.

“What Sen. Cruz did to Ben Carson was a disgrace and an insult to Dr. Carson and the process,” Lewandowski said. “What Sen. Cruz did to the voters of Iowa was also a disgrace in regard to their phony voter violation form. Additionally, they misrepresented Mr. Trump and unfortunately this happens all the time with crooked politicians.”

Asked whether the campaign planned to file a formal complaint, he said: “Wait and see.”

For all their bluster, the top tow of Cruz and Trump were keeping a wary eye on Iowa's surprisingly strong No. 3. Rubio's campaign said it had raised $2 million within 24 hours of Monday's results.