HOUSTON --- Three weeks after being pummeled on a debate stage in New Hampshire, Sen. Marco Rubio of Florida showed Thursday night that he had learned his lesson, launching repeated and aggressive attacks on front-runner Donald Trump in the hope of slowing the New York businessman's march to the nomination.
In New Hampshire, Rubio faltered under relentless attacks from New Jersey Gov. Chris Christie. On Thursday, it was as if he were channeling Christie's prosecutorial style. He unloaded a series of charges from Trump's past against the billionaire reality TV star.
He mocked his opponent as shallow on the issues. He needled him and interrupted him as Trump has interrupted others in past debates. It was the kind of performance his supporters had hoped he would deliver.
Rubio wasn't alone in challenging Trump at Thursday's debate. Sen. Ted Cruz of Texas, hoping to boost his candidacy after a disappointing third-place finish in last week's South Carolina primary, used his time to try to undermine Trump's conservative credentials and his electability.
Trump would be a high-risk nominee, Cruz charged, one whose inconsistencies on issues and past friendships with and contributions to Democrats would leave him vulnerable in the general election.
The question is whether any of it will change the minds of Republican voters ahead of two critical weeks in March in the Republican race. Though he found himself attacked from the two candidates on either side of him on the stage, Trump remained typically aggressive. "Swing for the fences," he taunted his rivals part way through the debate.
It was that kind of night for the Republicans - a night that repeatedly descended into personal insults, with the candidates shouting over one another.
Down to five candidates on the stage and with many seeing the race narrowing to Trump, Rubio and Cruz, rarely has there been a time when the stakes were as high. From here on, every Trump victory adds to his luster as the front-runner, and Thursday was the first moment for his rivals to change perceptions of where the race could be heading.
Neither Rubio nor Cruz has relished going after Trump in the past, perhaps fearing the blowtorch counterattacks that were leveled at others who are now on the political sidelines. But by Thursday night, they had no choice. Amid a rising Republican chorus urging them to go after the front-runner, the two answered the calls.
Rubio used his opening statement to issue an implicit attack on Trump. He argued that what Republicans need is a nominee who would carry both the conservatism and the optimism of former president Ronald Reagan into the general election, rather than "a party that preys on people's angers and fears."
That was only the start. Within minutes, he had charged Trump with building Trump Tower with illegal immigrants, of running "a fake university" and of becoming wealthy by inheriting a fortune.
"If he hadn't inherited $200 million, you know where Donald Trump would be right now?" Rubio asked. "Selling watches."
"I took $1 million and I turned into $10 billion," Trump replied.
They tangled over health care. Again borrowing from Christie's style, Rubio noted that as Trump described his plan for replacing the Affordable Care Act, the New Yorker was repeating his points over and over.
Cruz questioned whether Trump would nominate true conservatives to the Supreme Court. He jumped on a question to Trump about releasing his taxes and pressed him to prove that there is nothing lurking in his finances that could blow up in the middle of the general election. He accused Trump of talking out of both sides of his mouth on the Middle East and Libya.
Ohio Gov. John Kasich, as is his style, tried to stay above the fray, hoping that his promise to be practical and open to compromise with Democrats in order to solve problems will win him enough votes to keep his fragile hopes alive.
Rubio's performance Thursday will cheer those who have rallied to his side since South Carolina, despite the fact that he did not win any of the first four contests. But will that be enough to impress voters?
Super Tuesday begins a critical two-week stretch in the Republican campaign that will determine whether any of the remaining candidates can disrupt Trump's path toward the nomination.
Super Tuesday is the biggest day on the 2016 primary and caucus calendar, with contests in 11 states and 595 delegates up for grabs. Texas, with 155 delegates, offers the single biggest prize, followed by Georgia with 76.
To that point, delegates will be allocated on a proportional basis, meaning that candidates who finish relatively close to the winner will grab a share of the delegates. Beginning on March 15, however, the rules change. From there to the end of the primary season, states have the authority to award delegates on some version of a winner-take-all basis.
That makes March 15 especially important in sorting out the future of the nomination. March 15 is the second-biggest day on the calendar. Florida, Illinois, Missouri, North Carolina and Ohio, with a combined total of more than 350 delegates, hold primaries that day. By the end of that night, it should be clear which of the candidates, if any, has the strength and support to go up against Trump.
Those two weeks also pose individual tests for Cruz, Rubio and Kasich. Each must win his home state, at a minimum, to remain viable.
Cruz will be first in the barrel on Tuesday. Without a victory in his home state, Cruz's Southern and Super Tuesday strategy will collapse. He was damaged by his failure to win South Carolina last weekend, and a loss in Texas probably would finish him. But his advisers have expressed confidence about his ability to win in the Lone Star State.
Rubio's big test comes March 15 in Florida, where Trump has been leading the polls by a wide margin. But Rubio also must demonstrate his vote-getting appeal on Super Tuesday. Unlike Cruz, who was victorious in the Iowa caucuses, Rubio has not won a state, finishing third in Iowa, fifth in New Hampshire, and second in South Carolina and Nevada.
His campaign has benefited financially and in endorsements from the withdrawal of former Florida governor Jeb Bush. But Rubio is under pressure to translate that into the kind of support from the voters that pushes him to victory somewhere.
Kasich has set a big goal for himself ahead of his home state of Ohio. After his second-place finish in New Hampshire, his advisers said they would plant a flag in Michigan, making it something of a must-win.
For those fearful of Trump as the party's nominee, Thursday was supposed to be the night that the dynamic of the race began to change. Certainly Rubio and Cruz tried to make that happen, with some success. But Tuesday's balloting will be the real first test of whether things actually are changing.