Republican Senate candidate Joni Ernst of Iowa has a double-digit lead over her closest primary opponent in a new poll from Loras College. The survey of 600 likely Republican primary voters found Ernst, a state senator, with 30.8 percent support, while businessman Mark Jacobs comes in second with 19.3 percent support.

Sam Clovis and Matt Whitaker come in behind with 9.5 percent and 7.3 percent, respectively, while 29.2 percent remain undecided.

According to Real Clear Politics's poll average, Ernst now has a 6.7-point lead in the race. Jacobs is hitting back with a new ad out today criticizing Ernst's record in the state senate. The Iowa primary will be on June 3, and if the winner receives more than 35 percent of the vote, he or she will avoid a nominating convention. Loras College's Christopher Budzisz says in the polling memo that it's "highly unlikely that we are looking at a convention to decide the nomination" and that the race is likely to be a direct match-up between Ernst and Jacobs.

Ernst, who also serves as an officer in the Iowa Army National Guard, has been gathering momentum in recent weeks, first taking the lead over Jacobs in a Suffolk poll last month, aided by humorous, memorable TV ads like this one. Among those who have endorsed her campaign are Sarah Palin, Mitt Romney, the Senate Conservatives Fund, the Chamber of Commerce, the National Rifle Association, and Nebraska senator Deb Fischer.

Ernst, Jacobs, and the rest are vying to take on Democratic congressman Bruce Braley, his party's nominee to replace retiring Democrat Tom Harkin in the Senate. The general election is considered a toss-up.

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