TOPEKA, KAN. – Kansas Republicans on Tuesday nominated Rep. Roger Marshall to run for the U.S. Senate instead of polarizing conservative Kris Kobach, heeding the party establishment's advice for keeping a normally safe seat out of play in what could be a difficult year for the GOP.

Marshall prevailed in a crowded primary field with the backing of major farm, business and anti-abortion groups but without a pre-election endorsement from President Donald Trump sought by Senate Majority Mitch McConnell and others for the two-term congressman for western and central Kansas. Marshall overcame Kobach's reputation as a conservative firebrand and informal adviser to Trump.

Marshall will face Democratic state Sen. Barbara Bollier, a former lifelong moderate Republican who received national attention at the end of 2018 by switching parties.

Kobach, the former Kansas secretary of state, is nationally known for advocating restrictive immigration policies and alienated independent and moderate GOP voters in losing the Kansas governor's race in 2018. Marshall and his allies made that loss a key issue as he and Kobach battled atop the GOP field.

The race for retiring four-term GOP Sen. Pat Roberts' seat had national implications even though the GOP hasn't lost a Senate contest in Kansas since 1932. Republicans are trying to keep their 53-47 Senate majority with competitive races in other states, including Arizona, Colorado and Maine.

Marshall immediately called for party unity at a watch party at a winery southwest of his central Kansas hometown of Great Bend. He told his supporters that the GOP's Senate majority is at stake in his race and said he was strengthened by the contentious primary.

"I've always believed in this iron sharpening iron," Marshall said in his livestreamed remarks. "After this primary, our swords are sharp and our shields are thick."

In his concession speech, Kobach said that he had faced a "very steep, uphill struggle" after telling reporters earlier in the day that the GOP establishment had a recent history of crushing conservatives like him. But he urged Republicans to get behind Marshall.

Bollier is a retired Kansas City-area anesthesiologist, while Marshall is an obstetrician.

Marshall raised about $2.9 million and Kobach, a little more than $1 million. Bob Hamilton, the founder of a Kansas City-area plumbing company largely self-funded a campaign heavy on TV ads with $3.5 million in personal loans.

Those figures were all dwarfed by PAC spending in the primary, which totaled about $11 million.

Marshall, Kobach and Hamilton and eight other candidates made the field the largest for the GOP since the state began holding Senate primaries more than 100 years ago.

McConnell's first choice in the race was Secretary of State Mike Pompeo, a former Wichita-area congressman, but while Pompeo made multiple visits to Kansas suggesting interest, he definitely declared himself out in January.

Roberts declared his support for Marshall after the congressman had picked up key endorsements, including from political icon Bob Dole, 97, war hero, former Senate majority leader and 1996 GOP presidential nominee.