DAVENPORT, Iowa Marco Rubio concluded the first phase of a carefully calibrated presidential campaign Sunday, banking on a first strike in the Hawkeye State to boost his standing in the race for the Republican nomination.

The Florida senator, 44, delivered his closing argument to Republican voters in the state during a series of rallies and town hall meetings. Rubio highlighted the optimistic, future-oriented message at the heart of his campaign message and minimized negative attacks on his rivals that dominated in recent weeks as the contest grew heated. The Iowa caucuses begin at 8 p.m. Eastern Time on Monday.

"It has been a long road, and I can't believe we're finally here," Rubio told an evening rally of about 500 in Davenport, a community along the Mississippi River in eastern Iowa. "In 25 hours, you become the first Americans to decide what comes next after Barack Obama."

In a move that reflects a view that he is his campaign's best asset, Rubio appeared Sunday without guest speakers, except for the senator's Iowa campaign chairman, state Sen. Jack Whitver. Rubio kicked off each event with a pitch and instructions on how to caucus for him. The crowds were enthusiastic and Rubio's campaign staff expressed cautious optimistism that the senator would finish strong enough to contend in New Hampshire.

In the final Des Moines Register/Bloomberg Politics poll released just before the caucuses Rubio, at 15 percent solidly, was in third place, trailing New York celebrity businessman Donald Trump (28 percent) and Sen. Ted Cruz of Texas (23 percent). Rubio backers argue this finish would validate his campaign strategy and continue the momentum his bid has gained ahead of the Feb. 9 New Hampshire primary.

"I feel really good about where we're at, and I'm really proud of the campaign team that we've built in Iowa," Whitver told the Washington Examiner on Sunday. "I'm really proud of the race that Marco has run. Who knows what's going to happen on caucus night, but I feel pretty good about where we're at."

The Rubio campaign has said little about its Iowa voter turnout operation. But campaign sources concede that it can't match Cruz's ground game. Cruz is widely acknowledged to have the best field team in the state of any Republican candidate. But Rubio supporters say that its get-out-the-vote activities are more aggressive than realized.

On the eve of the caucuses, the Rubio campaign had four Iowa offices, in Sioux City, Davenport, Cedar Rapids and Ankeny, near Des Moines. They have 15 full-time paid staff on its state team, and college coalitions on the campuses of Iowa State University and the University of Iowa. The campaign was phone banking every evening and used up-to-date data analytics to motivate the most likely voters to caucus for Rubio.

The Rubio campaign contrasts a strategy they say aimed at timing the senator's rise with rivals who peaked early. Retired pediatric neurosurgeon Ben Carson jumped to the top of the polls in Iowa and nationally in October, only to tumble. He was running fourth, at 10 percent, in The Des Moines Register/Bloomberg Politics poll. Cruz rose to first in Iowa in November, only to drop down to second early this month.

Rubio also built his campaign around competing in all four early states, rather than betting heavily on one state. The reasoning was that the field was too deep to cede too much of the senator's destiny to one primary, as some candidates have in New Hampshire. The strategy was complicated by the nearly $30 million in negative advertising against Rubio unleashed by Cruz, former Florida Gov. Jeb Bush and their supportive super PACs.

But Rubio still has among the highest personal favorability ratings of GOP contenders. The campaign hopes that Iowa Republicans are poised to slingshot the senator past his competitors, and into a position where he starts winning. Rubio's advisors have meticulously managed expectations, but his Iowa supporters hope that he might do better than third place.

"He's going to do better than the polls say," said James Larsen, 55, a dentist from Bettendorf who plans to caucus for Rubio and showed up to see him in Davenport. "He's going to do very well.