In Iowa, a rare and unpredictable convention will pick the Republican nominee in one of the country’s most competitive House districts — and the results could determine whether Republicans hold the seat in 2014.  

None of the six Republican candidates received the 35 percent necessary to win the nomination outright  in the 3rd District. Instead, the nomination fight continues at a June 21 convention , in which hundreds of party activists select the nominee.  

It’s a process that has only happened twice in 50 years. The last time was in 2002, when now-Rep. Steve King, R-Iowa, won the nomination.  

“Any one of them could win legitimately,” said Doug Gross, a former chief of staff to Gov. Terry E. Branstad and a 3rd District convention delegate. “Anybody who tells you they can handicap that race is smarter than anyone around or is lying — one of the two. No one knows what is actually going to happen.”  

Although the convention is unpredictable, some GOP operatives in the Hawkeye State said the process gives them a second chance to avoid state Sen. Brad Zaun as their nominee. Zaun finished first with 25 percent in Tuesday’s primary, among a field of six candidates.  

Multiple Republican operatives in the state said Zaun ran a bad campaign in 2010 , when the then-GOP nominee lost to Rep. Leonard Boswell, D-Iowa, in the best election cycle for Republicans in decades. They added that past issues, including when Zaun allegedly banged on the window of an ex-girlfriend and called her a “slut,” won’t match up well with the Democratic nominee : former state Sen. Staci Appel.  

In order to win at convention, a candidate must receive more than 50 percent of the vote from the roughly 500 elected delegates in attendance. The process will likely go through multiple ballots, with the lowest vote recipient falling off  each successive ballot until there are only two candidates. The winner of that one-on-one matchup gets the nod.  

The six candidates who ran in the primary will spend the next two-and-a-half weeks engaged in old-school retail politics, wining, dining and courting delegates to win their support prior to the convention.  

Typically, GOP convention delegates hail from the conservative wing of the Republican Party. But GOP operatives said  this cycle, Branstad helped stack the convention with delegates . His efforts started when it looked like the state’s open Senate race was headed for convention , but the party avoided that Tuesday night with state Sen. Joni Ernst’s resounding victory.  

“Because of the efforts of Gov. Branstad, they diversified, broadened and brought in a lot of folks this time around who are in the category of the more pragmatic group of delegates, who look at this race a little differently than they have in the past,” said one former Branstad aide who is also a delegate at the 3rd District convention. “They’re looking at electability, and that might override ideological issues with each candidate.”  

Other candidates from Tuesday’s primary who are still vying for the nomination include bridge construction contractor Robert Cramer, a Christian activist with ties to social conservative Bob Vander Plaats. Cramer came in second-place on Tuesday with 21 percent.  

But GOP operatives said the state’s social conservatives were less successful in electing their delegates to convention and leadership roles in the party this year, which means Cramer could have a tough path to victory on June 21.  

Iowa Secretary of State Matt Schultz, who came in third in Tuesday’s primary with 20 percent, also appeals to the social conservative wing of the party. GOP operatives say Schultz is an engaging speaker, which could help him garner support at convention from the delegates.  

Iowa Renewable Fuels Association Executive Monte Shaw, who came in fourth in the Tuesday primary with 17 percent, is a known name in state politics. Shaw served as a two-term member of the State Central Committee — the governing body of the Iowa Republican Party — and chaired the 3rd District convention in 2012. His relationship with many of the party activists could also help him.  

Finally, former Capitol Hill aide David Young also has ties to the activists in the state because of his years serving as chief of staff to Sen. Charles E. Grassley, a monumental figure in Iowa Republican politics. Young came in fifth in the primary with 16 percent.  

The sixth candidate, teacher Joe Grandanette, earned just 2 percent of the vote Tuesday and is not expected to be a player at the convention.  

Whomever wins the nod willl face Appel in this southwestern Iowa district. President Barack Obama carried it by a 4-point margin in 2012.  

The contest is one of just seven House races rated a Tossup by the Rothenberg Political Report/Roll Call.