TOPEKA ? U.S. Sen. Pat Roberts, a power in Kansas politics for decades, faces a challenge in the Republican primary from a Kansas City-area doctor who’s never run for office but has gained attention in conservative and tea party circles for his vocal criticism of the federal health care overhaul.

Milton Wolf, a 42-year-old Leawood radiologist, announced Tuesday that he intends to run against Roberts, who’s seeking a fourth six-year term in the Senate.

Roberts also has been a strong critic of the 2010 health care law championed by President Barack Obama, a Democrat.

Wolf’s campaign issued a statement ahead of his formal announcement, saying the nation is “threatened by the politicians in Washington.”

“I’m here today to fight for our Constitution and the divinely-inspired American idea of individual liberty, limited government and free enterprise,” Wolf said in the statement. “I’m here today to reclaim the American Dream for all Kansans and all Americans.”

Roberts, 77, was first elected to the U.S. Senate in 1996, after serving 16 years in the House, representing the sprawling 1st District of western and central Kansas. He was an aide to the Republican who held the House seat before him, and his career in Washington began in 1969.

No Democrat has publicly announced plans to run for Roberts’ seat.

Wolf’s challenge could highlight divisions playing out nationally among tea party conservatives and others in the Republican Party. He launched his campaign Tuesday at the Ritz Charles reception hall in the Kansas City suburb of Overland Park and promised in his statement beforehand to fight to repeal the health care law and to oppose any increase in the federal government’s debt ceiling.

However, Roberts has drawn support throughout his career from all factions within the state GOP. Gov. Sam Brownback and fellow Kansas Sen. Jerry Moran are his campaign’s honorary chairmen, and he’s been endorsed by every member of the state’s all GOP-congressional delegation, including perhaps its most conservative member, 1st District Rep. Tim Huelskamp, a tea party favorite.

Roberts has been amassing public endorsements from Republican officials for weeks, and his campaign ended June with nearly $1.5 million in cash on hand. His re-election campaign also noted Tuesday that he’s consistently received strong ratings from conservative, anti-abortion and gun rights groups.

Leroy Towns, Roberts’ executive campaign manager, said it would be “really difficult” for a primary challenger to be more conservative than the senator.

“He’s respected and liked,” Towns said. “Dr. Wolf’s got a huge hill to climb.”

Wolf also has received attention nationally because he and his campaign describe him as a second cousin, once removed, to the president. His campaign said Tuesday that Wolf’s mother and Obama’s maternal grandmother were cousins.