PORTLAND — A pediatric neurosurgeon has formally joined the race for the Republican nomination to challenge Democratic U.S. Sen. Jeff Merkley.

PORTLAND — A pediatric neurosurgeon has formally joined the race for the Republican nomination to challenge Democratic U.S. Sen. Jeff Merkley.

Monica Wehby of Portland announced her decision Tuesday, saying in a press release that the state's pioneer spirit "is under attack by a federal government that wants to control every aspect of our lives."

Among those Wehby will compete against in the May primary are state Rep. Jason Conger, R-Bend, and Bend businessman Sam Carpenter.

Wehby's medical background is likely to define her candidacy. In 2004, she was the chief petitioner of Ballot Measure 35, which would have limited non-economic damages in medical lawsuits. Voters narrowly defeated the measure.

As for the Affordable Care Act, Wehby said she opposes the requirement that individuals buy health insurance, and the rollout is exposing other weaknesses.

"There's a lot of problems with the law and I think that's what happens when you push it through, so I think there's a lot of things that have to be addressed," Wehby told The Oregonian.

Whoever emerges from the crowded GOP field will be a longshot to beat Merkley in a state where Democrats outnumber Republicans by more than 180,000 voters. No Republican has won a statewide race in Oregon since 2002, and the Merkley campaign has raised $2.3 million.

"Because of party registration none of these candidates will be close to Merkley in the initial and developing public opinion polls," said Jim Moore, political science professor at Pacific University. "This is Merkley's first defense, thus it is his most vulnerable time. We haven't seen him on the list of vulnerable candidates."

Wehby, 51, grew up in Tennessee before studying at Notre Dame and Baylor. The Catholic mother of four moved to Portland 15 years ago to work at Randall Children's Hospital at Legacy Emanuel Hospital.