TOPEKA, Kan. (AP) — Kris Kobach, nationally known as an advocate of tough immigration policies and a vocal supporter of President Donald Trump, launched a campaign Monday for the U.S. Senate in Kansas amid tepid support from some Republicans who voiced concern that his recent loss in the governor's race could threaten the party's majority.

Kobach filed paperwork with the Federal Election Commission creating a campaign committee for a run at the Republican nomination next year and planned to make a speech Monday afternoon in Leavenworth, outside the Kansas City area. He is seeking the seat held by four-term GOP Sen. Pat Roberts, who is not running for re-election.

Kobach, the former Kansas secretary of state, confirmed in January that he was considering the Senate race, shortly after Roberts announced his plans. Some Republicans also speculated that he could land a prominent job in Trump's administration, but that hasn't materialized.

A spokesman for the National Republican Senatorial Committee, the political arm of the Senate GOP, made clear that the group opposes Kobach's candidacy. Republicans would be highly favored to retain Roberts' seat and they don't want to risk putting it in play as they defend their 53-47 majority in the chamber in next year's elections.

"Just last year, Kris Kobach ran and lost to a Democrat," said the spokesman, Jesse Hunt. "Now, he wants to do the same and simultaneously put President Trump's presidency and Senate majority at risk. We know Kansans won't let that happen and we look forward to watching the Republican candidate they do choose win next fall."

Even though Kobach's candidacy is likely to upset some fellow Republicans, he retains support among conservatives, particularly advocates of tough policies against illegal immigration. Kobach has long alienated GOP moderates, but even some conservatives soured on him after he lost the governor's race to Democrat Laura Kelly.

"The last statewide campaign that Kris ran for governor could be described as disorganized and amateur at best," said Kansas Senate Majority Leader Jim Denning, a conservative Kansas City-area Republican. "We simply can't afford to give the Democrats another gift like we did with Laura Kelly in that governor's race."

Kobach's paperwork initially misspelled his first name as "Chris," but it was corrected two minutes later.

Republicans haven't lost a U.S. Senate race in Kansas since 1932, and Kobach's supporters say his national profile on immigration would help in a race. Trump endorsed Kobach in last year's race for governor.

Earlier this year, with Kobach mulling the race, some top Republicans nudged U.S. Secretary of State Mike Pompeo, a former Kansas congressman, to enter the Senate race, but he said he was focused on his job as the nation's top diplomat.

If Pompeo stays out, the race for the GOP nomination could become crowded. State Treasurer Jake LaTurner and Dave Lindstrom, a Kansas City-area businessman and former Kansas City Chiefs player, already are campaigning.

Other prospective candidates include U.S. Rep. Roger Marshall, of western Kansas; Kansas Attorney General Derek Schmidt; Kansas Senate President Susan Wagle, of Wichita; former Gov. Jeff Colyer, ousted in the primary last year by Kobach; Wink Hartman, a Wichita businessman who ran for lieutenant governor on Kobach's ticket; Matt Schlapp, chairman of the American Conservative Union, and Alan Cobb, president and CEO of the Kansas Chamber of Commerce.

Among Democrats, Barry Grissom, a former U.S. attorney for Kansas, and ex-U.S. Rep. Nancy Boyda of northeast Kansas have launched campaigns.

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Associated Press writer Alan Fram also contributed from Washington.

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