Sen. Marco Rubio (R-Fla.) came out swinging during the CNBC debate and had some big applause lines. See his most memorable moments of the third Republican debate. (Jhaan Elker/The Washington Post)

For most of this year, Sen. Marco Rubio (Fla.) and Sen. Ted Cruz (Tex.) have been lurking in the background of the Republican presidential campaign. On Wednesday night, they broke out into the open, delivering strong and forceful performances in a raucous and rambling Republican debate marked by squabbling and sharp elbows.

Both Rubio and Cruz have won modest plaudits for their performances in the first two debates, but there was a demonstrable difference in what unfolded on the stage at the University of Colorado. They outshone Donald Trump and Ben Carson, the leaders in the polls, and Rubio overshadowed his onetime mentor, former Florida governor Jeb Bush.

Whether this was a unique moment for Rubio and Cruz or a foreshadowing of where the Republican nomination contest is heading is a matter of speculation, with the voters the ultimate arbiters starting early next year. But both candidates served notice Wednesday that they are ready for the next phase of a rapidly changing and increasingly fractious campaign.

Trump more than held his own, improving on his performance in the second debate, in which he faded during the final hour. He showed little of the frustration that has been on display lately on the campaign trail. Carson was typically low-key, a style that has benefited him during the campaign even as his ideas and background face increased scrutiny.

But in the end, the two first-term senators from two of the most-populous states in the country might have gained the most, in part because each is seen among many GOP strategists as poised to rise to greater prominence in the race.

Republican presidential candidates sparred over experience, took jabs at their Democratic opponents and even shared a few laughs during CNBC's main debate in Boulder, Colo., on Oct. 28. (Sarah Parnass/The Washington Post)

In Republican circles, Rubio has been the focus of the most attention to date, despite relatively weak poll numbers and more potential than actual performance. He probably gained considerable credibility Wednesday night, particularly with fundraisers. Whether he can convert that into popular support remains the biggest question about his candidacy.

Rubio long has had the potential to become a crossover candidate, capable of corralling the support of mainstream conservatives and wealthy fundraisers, and able at the same time to tap into the frustrations of the GOP’s tea party wing. That remains his strongest calling card, if he is able to build from here.

Cruz occupies a different space in the GOP race: the hard-line conservative who has worn as a badge of honor his battles with Republican leaders in Washington and regularly espousing his belief that what the party needs is a nominee who can genuinely articulate the conservative principles that much of the base embraces.

Rubio arrived knowing he would come under attack, and he was well prepped. His strongest moment occurred when he was asked about his absenteeism in the Senate and his obvious disdain for a body he joined less than five years ago.

Responding to a question about an editorial in the South Florida Sun-Sentinel that was headlined, “Marco Rubio should resign, not rip us off,” Rubio turned the issue back on the news organization by pointing to Bob Graham, John F. Kerry and Barack Obama, all of whom ran for president while in the Senate and missed scores of votes. Rubio said none of them drew the ire of the newspaper in the way he has.

“This is another example of the double standard that exists in this country between the mainstream media and the conservative movement,” he said.

Bush sought to piggyback on the question, claiming that Rubio was working “like a French work week” and that he owed his constituents much more. “You can campaign or just resign and let someone else take the job,” Bush said.

10 charts explain the third GOP debate

Rubio took Bush’s question and went on the offense, accusing his rival of trying to take him down to save his own campaign. “The only reason why you’re doing it now is because we’re running for the same position, and someone has convinced you that attacking me is going to help you,” he said.

Cruz seized the stage a few minutes later with an attack on the CNBC moderators, claiming that the round of opening questions to Trump, Carson, Kasich, Rubio and Bush were biased and had nothing to do with the country’s problems.

“The questions that have been asked so far in this debate illustrate why the American people don’t trust the media,” Cruz said. “This is not a cage match.”

Cruz also drew a contrast with the recent Democratic debate, saying those candidates had drawn only fawning questions. “Nobody watching at home believed that any of the moderators had any intention of voting in a Republican primary,” he said.

Attacks on the media have been a staple of past Republican debates, and Cruz’s sharp words drew huge applause from the audience inside the Coors Events Center and stirred strong positive reaction on social media and, no doubt, among the disgruntled conservatives whom he has courted almost from the moment he arrived in the Senate a few years ago.

The debate sprawled over economic and other topics, and other candidates had times when they sought to take the spotlight. Most of the candidates played to type Wednesday night. All could point to moments when they made their points effectively.

Bush stressed his record in Florida and said he would shake up Washington but do it in a way that brought people together. But he got the worst end of the exchange with Rubio, no doubt to his detriment.

Ohio Gov. John Kasich opened with a screed against Trump and Carson as unqualified to serve as president, and he said it was time to end the “fantasy” of what they were saying and look to people with records of accomplishment.

New Jersey Gov. Chris Christie and former Arkansas governor Mike Huckabee continued their debate about the future of Social Security.

Sen. Rand Paul (Ky.) railed against the new budget deal brokered by outgoing House Speaker John A. Boehner (R-Ohio) and the White House and pledged to filibuster it.

Carly Fiorina, who used two previous debate performances to raise her profile and, temporarily, her poll numbers, defended her tenure as chief executive at Hewlett-Packard and said she would be as tough on Hillary Rodham Clinton as any other potential GOP nominee.

Wednesday’s debate was at times unmanageable. Candidates showed only minimal respect for the rules, and the moderators provoked the anger of the candidates. Candidates spoke over one another repeatedly, especially in the early stages.

The third debate of the pre-primary season came at a time when two of the outsiders in the crowded field continued to dominate the Republican race. But it also came at a time of volatility and greater uncertainty than a month ago, as some national and state polls began to shift away from Trump and toward Carson.

With fewer than 100 days before the voting begins in Iowa in early February, the GOP contest has moved into a more intensive phase. For a number of the candidates lagging in the polls or performing below expectations, the sense of urgency was apparent on the stage Wednesday night in Boulder.

The Republican race has defied almost everyone’s expectations this year, and there is no consensus among veteran Republican strategists about what the future holds. Wednesday’s debate might have offered a preview of what’s to come.