CEDAR FALLS, Iowa — Marco Rubio on Sunday urged late breaking Republican voters here to join his campaign to grow the conservative movement and put Republicans back in charge of the White House in November.

The Florida senator is gunning for a strong third place in Monday's Iowa caucuses in the midst of millions in paid television attacks from rivals Sen. Ted Cruz of Texas and the super political action committee supporting former Gov. Jeb Bush of Florida. Rubio is fighting back by pitching voters on his ideological conservatism and ability to coalesce conservatives and mainstream Republicans and convert voters to the cause among an electorate that tilts Democratic in national elections.

"No one can bring the conservative movement and Republican party back together faster than I can," Rubio told a standing room-only crowd of nearly 500 on the campus of Northern Iowa University. "I don't just want to bring it back together; I want to grow it."

The Des Moines Register/Bloomberg Politics poll conducted last week put Rubio at 15 percent, in third place behind New York celebrity businessman Donald Trump and Cruz, who stood at 28 percent and 23 percent, respectively. The campaign is trying to temper expectations, and privately is holding fast to its prediction of a third place finish, and hopeful that Rubio comes in at 15 percent or higher.

Rubio on Sunday held his final town hall before the caucuses in Cedar Falls, in eastern Iowa, before heading to Cedar Rapids and Davenport for campaign rallies.

The Des Moines Register/Bloomberg poll showed Rubio with among the highest favorability rating of any candidate, at a net positive of 49 percent. The campaign's challenge with a little more than 24 hours to go is to build on the senator's momentum and convert late deciders and others wavering between the Floridian and Cruz. In interviews with the Washington Examiner since early last week, most Rubio leaners have designated Cruz as their other choice.

Scott Abels, who showed up to Rubio's town hall at Northern Iowa University with his wife and son, is one such likely caucus-goer. The 45-year-old production planner from nearby Evansdale has never caucused before, and said he's leaning Rubio because "I trust him more."

"He seems more honest, open, seems to have all the answers right," Abels said. "He looks like he's done his homework."