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URBANDALE, Iowa -- Florida Sen. Marco Rubio rallied supporters at a cookout in Iowa Monday night alongside U.S. Senate candidate Joni Ernst on the eve of that state’s primary election.

“[Ernst] is an exceptional candidate,” Rubio told the crowd. “Come November, the whole country may be up late watching the returns from Iowa because the choice you make here could very well be the difference between another two years with [Nevada Sen.] Harry Reid as majority leader or a new day for our country. We have the opportunity to reclaim the American dream.”

As attendees munched on pork sandwiches in the parking lot outside the Ernst campaign headquarters, Rubio spent time making his way through the crowd, shaking hands and signing autographs.

This campaign event was Rubio’s first trip back to Iowa since keynoting the annual birthday bash in honor of longtime Iowa Gov. Terry Branstad just days after the 2012 election -- helping fuel speculation about his 2016 presidential ambitions.

Asked about his return to Iowa Monday, Rubio denied having scheduled any other meetings in the state, noting he was only there to help Ernst get elected.

U.S. Sen. Marco Rubio, R-Fla., is greeted by Iowa Republican senatorial candidate Joni Ernst, right, before speaking at a rally with Ernst supporters, Monday, June 2, 2014, in Urbandale, Iowa.Charlie Neibergall / AP

The first-term Florida senator is just one of the potential 2016 presidential contenders to partake in the key senate race in the Hawkeye State. Former Pennsylvania Sen. Rick Santorum, who also won the 2012 Iowa Caucus, endorsed and participated in a television ad for Sam Clovis, a conservative radio talk host. Texas Gov. Rick Perry, who also attempted a presidential bid in 2012, campaigned alongside former U.S. Attorney Matt Whitaker last week.

Both Mitt Romney, the 2012 Republican presidential nominee, and former Alaska Gov. Sarah Palin have also endorsed and campaigned alongside Ernst.

Discussing the wide range of endorsements Ernst has netted, Rubio said that "not only is she able to unify our party but she is able to hopefully unify Americans to bring them together after six years of deeply divisive rhetoric coming out of the White House and the Senate."

Five Republicans are vying for the GOP nomination to run against Democratic Rep. Bruce Braley in November for the open senate seat. Ernst, a state senator and Iraq war veteran, would become the first women to serve Iowa in Congress if elected.

Recent polling shows Ernst as the clear frontrunner in Tuesday’s primary, but she needs to win at least 35 percent of the vote to avoid the nomination being decided at a state convention.

“I do feel very good,” Ernst said. “I feel very good about tomorrow, however I am going to continue to work like I am 10 points behind. We are going to push all the way until 9 p.m. tomorrow night when polls close.”