Republican presidential candidate Marco Rubio (R-Fla.) speaks to campaign volunteers through a bullhorn at the Team Marco Orlando headquarters March 13 in Orlando, Fla. (Win McNamee/Getty Images)

MELBOURNE, Fla. – Sen. Marco Rubio, barnstorming his home state Monday in a last-gasp effort to spring an upset over Donald Trump, said the mogul’s abrasive rhetoric has already earned him a spot in history — for all the wrong reasons.

“I don’t think there’s anyone in the history of American politics that compares to the vulgarity of a Donald Trump candidacy,” Rubio told reporters here. He repeated himself to emphasize his point: “In the history of American politics.”

Before that, the Florida senator campaigned outside a restaurant here where supporters held up signs and chanted his name. Sleeves rolled up, under the bright sunshine, Rubio encouraged his backers to keep fighting for him, and he framed Tuesday’s primary as a chance to go one of two very different directions.

“Tomorrow is a choice between optimism and fear,” Rubio told the crowd.

Every recent public poll has showed Rubio trailing Trump, including new numbers out Monday morning. His supporters fear that a loss would effectively end his campaign.

Rubio defended his strategy for dealing with Trump. For most of his campaign, he responded to Trump only when asked about him by a reporter. Late in the race, he went after him with a barrage of deeply personal insults he has since said he regrets.

“We also had to spend time telling people who we were, in the hopes that voters would see through this and eventually reject it, and obviously that to this point has not worked as well as we hoped,” acknowledged Rubio in a strikingly blunt manner.

At one point, Rubio spotted someone holding up a Bernie Sanders sign. “Don't worry, you're not going to get beat up at my rally,” said Rubio, referencing the violent clashes at Trump’s recent rallies and the businessman’s threat to encourage his supporters to protest the Vermont senator and Democratic White House hopeful.

Rubio, who seemed more upbeat than he was over the weekend, started his day in Jacksonville and is making his way south in his campaign bus along I-95. His final stop of the day is scheduled for 9 p.m. in West Miami, where he launched his political career as a city commissioner.

Rubio said over the weekend that it is becoming more difficult to live up to his pledge to support Trump if he is the Republican nominee. He reiterated his position here in Melbourne.

“It’s getting harder every day,” Rubio said.