Iowa Republicans will choose their nominee to replace retiring Rep. Tom Latham (R-Iowa) in a convention, after no candidates managed to reach 35 percent of the vote.

The Associated Press has called a convention for the crowded field. Iowa state Sen. Brad Zaun (R) led the pack with 25 percent of the vote, though the final tally won't matter at the convention and five candidates were above 15 percent of the vote with 96 percent of precincts reporting.

The winner will advance to face former Iowa state Sen. Staci Appel (D) in a swing district that is a top priority for both parties.

Establishment Republicans would normally worry about a convention, as conservative activists have dominated Iowa's GOP party conventions. But Iowa Gov. Terry Branstad (R) helped engineer a coup of the state party and many of his more centrist loyalists will be at the convention this year.

Across the state, Iowa state Rep. Patrick Murphy (D) and businessman Rod Blum (R) will face off for Rep. Bruce BraleyBruce Lowell BraleyOPINION | Tax reform, not Trump-McConnell feuds, will make 2018 a win for GOP Ten years later, House Dems reunite and look forward Trump: Ernst wanted 'more seasoning' before entertaining VP offer MORE's (D-Iowa) seat after winning their primaries.

The Associated Press has called the race for Murphy and Blum. Murphy led his five-way primary with 36 percent of the vote and 85 percent of precincts reporting, while Blum led his three-way primary with 55 percent of the vote and 85 percent of precincts reporting.

Murphy is favored in the general election in the Democratic-leaning eastern Iowa district.

This post was updated at 12:30 a.m.