TAMPA, Fla. — "Keep Calm. Vote Rubio."
It was the directive supporters waved on poster boards behind Rubio at his Tampa rally Monday night, and perhaps the only option remaining for fans of the Florida senator as his flagging campaign makes what could be its final push the week before his home state's pivotal primary vote.
Having suffered defeats in every state that voted Saturday after a disappointing showing on Super Tuesday last week, Rubio and his allies have since found small solace in an outright win in Puerto Rico on Sunday, and with it the commonwealth's 23 delegates.
Though Rubio has insisted he'll take the GOP primary fight all the way to the party's convention, most observers see little chance for him to remain in the race if he doesn't pull out a win in his home state, and that still remains in doubt.
A new poll out Monday, by Monmouth University, seemed to show the race narrowing, with Rubio just eight points behind frontrunner Donald Trump among Florida likely GOP voters. But Trump unleashed a new attack ad that same day that paints Rubio as "dishonest," and Ted Cruz is making a play in Florida to siphon votes from Rubio in hopes of delivering him a knockout punch in his homestate.
Rubio implicitly acknowledged the make-or-break nature of the Florida fight during his rally.
"So! It always comes down to Florida," he said with a grin, to open his speech.
Rubio himself was, outwardly, keeping calm, telling reporters that he felt confident in his chances because he had been in this same underdog position before, during his 2010 Senate race against then-Gov. Charlie Crist.
"Donald reminds me a lot of Charlie Crist, a guy who was ahead of me significantly — actually, it reminds me of him because he supported him, he paid Charlie Crist a lot of money when he was running against me. But I feel good about the direction of things," he said.
Rubio said he had been in the underdog role "my entire life…and it's a role I'm comfortable with and feel good about where it's gonna lead." During the rally he hammered that same theme, telling the crowd his parents, too, were "underdogs" when they came to the U.S., but "they didn't give up — they persevered, they fought on."
And he dismissed the new attack ad from Trump as "almost identical to the attacks Charlie Crist used against me in 2010."
"And that doesn't surprise me, Donald Trump was a huge supporter of Charlie Crist when I ran against him. So people in Florida are aware of all those things. They've all been looked at up and down back and forth in 2010 and even very recently. I don't think they're going to have an impact," he said.
Still, Trump's momentum is hard to dismiss, and the clearest evidence of the challenges facing Rubio in his final week came Monday night, when he turned out a crowd of about 1,100 in the same city where Trump brought out more than 10,000 just a few weeks prior.
Rubio, however, insisted "a lot of people come out to watch the show" Trump puts on, and said he wasn't phased by crowd size.
"If crowd size was indicative of his support, he would be blowing everyone away everywhere, he's now starting to lose states," he said.
He added that he believes the attacks he and others have launched against Trump are starting to take their toll on the candidate, and that Trump "suffered some real damage over the last week."
"People are starting to learn that Donald Trump the character and Donald Trump the person are not the same thing. And what you get as president is not the character you see on television, it's the person," he said.
"So I think as more and more people are learning about him, he's starting to run in some real resistance and obviously it's starting to impact him a little bit."
This story originally appeared on NBCNews.com.