State and federal candidates are heading into the final hours of the campaign for support in party primaries on Tuesday.

A Des Moines Register “Iowa Poll” released Saturday night found Joni Ernst had the support of 36 percent likely voters in the race of the Iowa GOP’s U.S. Senate nomination. Ernst led competitors Mark Jacobs, Matt Whitaker, Sam Clovis and Scott Schaben by double-digits.

The poll also found 16 percent of voters hadn’t picked a candidate. University of Iowa political science professor Tim Hagle says since primary elections attract just a fraction of those who vote in a presidential election, many of those undecided voters may wind up staying home.

“So it’s really a little bit hard to say and we just have to wait and see — and I’m certainly not to going try to make any prediction as far as what’s going to happen,” Hagle says, with a laugh. “It would seem that Ernst is the best position to potentially get to that magic 35 percent.”

A candidate in any party primary in Iowa must get at least 35 percent to win the nomination. It that doesn’t happen, delegates at a nomination convention decide whose name will be on November’s ballot.

“Convention delegates often give a lot of deference to who actually was the top vote-getter in the primary,” Hagle says.

And that was the case in Iowa’s last nomination convention, when Republican delegates in what was then Iowa’s fifth congressional district chose Steve King as their nominee in 2002. King, who won the nominating convention after three rounds of voting, finished the primary with 29.9 percent of the votes cast.

There are also primaries this Tuesday in three of Iowa’s four congressional districts. Congressman Bruce Braley has no opposition in the Democratic Party’s U.S. Senate primary. The seat has been held by Democrat Tom Harkin for three decades. Since Braley’s U.S. House seat is open, five Democrat and three Republicans have been traversing northeast Iowa’s first district, hoping to cross the 35 percent threshold to win their party primaries.

Republican Congressman Tom Latham announced in December he would not seek reelection. Two Democrats and a half dozen Republicans are competing to run in Latham’s southwest district. In the second congressional district in southeast Iowa, two candidates are competing for the Republican nomination and the chance to face-off against Democratic Congressman Dave Loebsack in November.

Among the 23 candidates running in Iowa’s competitive senate or congressional primaries this year, six are women.

“And I think it’s exciting from the fact that Iowa has never sent a woman to congress. I think we’ve got a lot of women this year who are viable candidates and I’m as optimistic as I’ve ever been that we will send a woman to congress this year,” says Dianne Bystrom, director of the Carrie Chapman Catt Center for Women and Politics at Iowa State University.

The polls open at 7 a.m.for Tuesday’s primary voting and close at 9 p.m.

Radio Iowa