Mr. Feenstra will face J.D. Scholten, a Democrat and former minor-league baseball player who lost the 2018 general election to Mr. King by just 10,000 votes. Democrats believe Mr. Scholten could beat Mr. King, but would have far tougher odds against Mr. Feenstra.
On the Democratic side in Iowa, voters on Tuesday chose Theresa Greenfield, a businesswoman who has proved to be an able fund-raiser, to face Republican Senator Joni Ernst. The race is expected to be among the most expensive Senate contests in the country, with outside groups already reserving $35 million in TV advertisements this summer and fall.
In Indiana, Republicans in the state’s Fifth Congressional District, which includes the northern swath of Indianapolis and counties to the north, picked Victoria Spartz, a self-funding Ukrainian-born state senator. She was one 15 candidates to replace Representative Susan Brooks, a Republican who is retiring. Democrats nominated Christina Hale, a state House member, for a race they believe will be competitive in November.
Democrats in Northern New Mexico appeared to be rejecting a congressional bid by Valerie Plame, the former C.I.A. agent outed during the George W. Bush administration. She was running a distant second with about 35 percent of the voted counted.
Representative Greg Gianforte, a Montana Republican who lost the 2016 governor’s race to Steve Bullock, defeated Tim Fox, the Montana attorney general, in a second bid to be governor. Mr. Gianforte made national headlines in 2017 when he pleaded guilty to misdemeanor assault for attacking a reporter. Mr. Gianforte will face Lt. Gov. Mike Cooney.
Mr. Bullock, a Democrat, cannot seek re-election and won his party’s nomination to challenge for the Senate seat currently held by Republican Steve Daines.
And in Ferguson, Mo., voters elected the first African-American and first woman as mayor of the city that was roiled by protests and civil unrest after police fatally shot Michael Brown, an unarmed black teenager.