As Donald Trump spent eight months marching a parade of insults over any and all detractors, Marco Rubio survived by staying mostly on the sidelines.

Rubio suddenly and urgently emerged from the shadows to hammer the front-runner on Thursday during the 10th Republican presidential debate. Florida's junior senator compared Trump to a sketchy sidewalk salesman in New York City, accused him of hypocrisy for hiring the undocumented workers he now wants to deport, and ridiculed the former reality TV show host for failing to articulate health-care policy details.

The sudden blast of aggression from Rubio standing on Trump's right—fortified by a steady stream of attacks from Ted Cruz on the front-runner's left—appeared to finally pierce the armor Trump built out of supreme confidence, snappy punchlines and a willingness to bully anyone that crosses his line. 

"A con artist is about to take over the Republican Party and the conservative movement and we have to put a stop to it," Rubio said on Friday on CBS, explaining his new aggressiveness. "The media is pumping him up as some sort of unstoppable force." 

But with Trump having dispatched so many foes in this race and winning convincing victories in three of the first four nominating contests, the question is whether it's too late to matter for his remaining rivals. The single biggest day of voting in the Republican primary is on Tuesday, when about half the delegates needed to secure the nomination are up for grabs.

"Trump ain't near dead," said former Texas Land Commissioner Jerry Patterson, a Republican who has endorsed Rubio, adding that the cumulative effect of attacks may have at least drawn some blood. "Several hundred small arms rounds can bring down an aircraft just as a well as one missile."

This wasn't the first time Trump has faced intense attacks during a debate. But in past meetings, he not only survived, but thrived in the confrontations. And his attackers—Rick Perry, Lindsey Graham, Carly Fiorina and, most recently, Jeb Bush—have all dropped out.

But it was the first time Rubio aggressively engaged. In a race that has never rewarded patience, the first-term senator stuck to a strategy of trying to avoid Trump's stream of invectives while out-lasting rivals like Bush and Perry, who, like Rubio, also appeal the party's traditional pro-business base. As recently as Wednesday, Rubio dodged when asked why he wasn't taking on Trump.

"I don't have any voters begging me to attack anyone," Rubio said in an interview on NBC's "Today Show," dismissing the question as a "media narrative." "I'm not in this race to attack any Republican."

Rubio finally showed he had the skills to take on Trump. But heading into the debate, the chances for either Rubio and Cruz to eclipse him in the nomination race seemed to be slipping away.

Rubio has a distant second to Trump in the past two nominating contests in Nevada and South Carolina, raising questions about whether he could ever win a state. A Quinnipiac poll released Thursday showed Trump with support of 44 percent of likely voters in Rubio’s home state of Florida. Rubio was second in the poll with 28 percent.

Cruz is also on the ropes. His home state of Texas holds its primary on Tuesday, and he’s been forced to defend his turf. A Feb. 24 poll from Emerson College showed Cruz up by just 1 percentage point against Trump, while a Monmouth poll a day later showed the Texan up by 15 points.

In the debate on Thursday, Rubio used a slightly different tactic than his predecessors, doing his best Trump impression by repeatedly talking over the front-runner, constantly interrupting and refusing to stop as Trump grew frustrated. Rubio was so persistent that Wolf Blitzer, the CNN anchor who moderated the debate, even once gently scolded Florida's junior senator.

"If Donald Trump hadn't inherited $200 million, do you know where he'd be right now? Selling watches in Manhattan," Rubio said early in the debate, held at the University of Houston's Moores Opera House.

The sheer number of different attacks launched by Rubio and Cruz may make it difficult for any of the competing messages to stick with voters, Patterson said.

Rubio seemed to understand this point, urging viewers to corroborate his claims on the Internet.

Go online and Google it,” Rubio said. “Donald Trump, Polish workers. You'll see it.”

Both Cruz and Rubio also tried to press Trump on policy, suggesting that he lacked the depth needed to be commander-in-chief.

In one exchange, Rubio pressed Trump for details on how he would repeal and replace Obamacare, beyond allowing insurance companies to compete across state lines. "This is not a game. What is your plan? What is your plan on health care?" Rubio asked.

But Trump kept stressing that his plan involves getting "rid of the lines around each state."

Rubio, who collapsed in the New Hampshire primary earlier this month after a debate performance in which he kept repeating the same talking points, smiled. "Now he’s repeating himself,” Rubio said, talking over Trump.

When Dana Bash, another CNN moderator, stopped the bickering between the two, she gave Trump more time. "Is there anything else you would like to add to that?" she asked Trump. 

"No, there's nothing to add," Trump said. "What is to add?"

The constant fire between Trump, Cruz and Rubio left the other two debate participants—retired neurosurgeon Ben Carson and Ohio Governor John Kasich—mostly out of the action.

“Can somebody attack me, please?” Carson said in an attempt to get involved.

Cruz tried to increase the pressure on Trump, too. Early on, he jabbed at Trump for giving campaign donations to lawmakers who wrote the 2013 Senate immigration reform bill, saying the businessman was missing in action during the debate. "Where was Donald? He was firing Dennis Rodman on Celebrity Apprentice," Cruz said.

Trump's frustration was visible as he pursed his lips, shrugged his shoulders and rolled his eyes throughout the evening.

But he also landed plenty of his own shots and one-liners. Told that the two past presidents of Mexico have said their country will never pay for a border wall, as Trump has insisted, Trump said, "The wall just got 10 feet taller."

He fought back against charges that he hired undocumented workers, saying "I'm the only one on the stage that's hired people."

"You haven't hired anybody," Trump said to Rubio. "You haven't hired one person, you liar."

"Your politicians—all talk, no action—I've been watching it all my life," Trump said. "This guy's a choke artist and this guy's a liar."

Trump, 69, then managed to twist knives simultaneously into the pair of first-term senators in their mid-40s.

"He can't do it for the obvious reason, and he can't do it because he doesn't know how to tell the truth," Trump said. "Other than that, I rest my case."

-- With assistance from Toluse Olorunnipa in Washington.

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