Sen. Marco Rubio (R-Fla.) will travel to Iowa to campaign for U.S. Senate candidate Joni Ernst (R) on Monday, a day ahead of the Republican primary there, a campaign aide told Post Politics.

Rubio has endorsed Ernst and his PAC launched a TV ad for her this week. An army of tea party and establishment Republican groups and activists have lined up behind Ernst, including Sarah Palin and Mitt Romney; the latter campaigned with Ernst Friday.

Ernst is the front-runner ahead of Tuesday's primary, polls show. Her main competition is self-funding businessman Mark Jacobs.

If no candidate in the crowded field receives more than 35 percent of the vote on Tuesday, GOP activists will choose their nominee at a convention.

The winner will likely face Rep. Bruce Braley (D) in the general election. The two parties are competing for the seat of retiring Sen. Tom Harkin (D).

The news of Rubio's trip was first tweeted by the Des Moines Register.