Democrat Jeff Merkley of Oregon probably isn't the first sitting senator Republicans think they can defeat this November. After beating incumbent Republican Gordon Smith in 2008 by 3 percentage points, Merkley appears safe in his seat. In 2012 Oregon voted for Barack Obama by more than 12 points, and the Cook Political Report rates the Senate race as "solid Democratic."

Merkley is a dedicated liberal who fits a state increasingly defined by its biggest city, the insufferably hip and progressive Portland. How can the GOP hope to take back this seat? One Republican challenger appears to be focusing on Merkley's vote and support for Obamacare. Monica Wehby, a pediatric neurosurgeon, has a new ad that juxtaposes news coverage of Oregonians who have had health insurance plans canceled to Merkley's promise in 2009 that under Obamacare, citizens would "have the choice of sticking with the plan you have."

"If you like it, it will absolutely be there," Merkley added. Watch the ad below:

The ad also features interviews with Oregonians who lost their insurance and excerpts from a speech Wehby made last month at Portland State University. The ad ends with a catchy slogan: "Keep your doctor. Change your senator."

Obamacare may be a potent issue in Oregon this year. One Democratic congressman from the state, Kurt Schrader, has already publicly criticized President Obama for the central "if you like your health insurance, you can keep it" promise made during the Obamacare debate four years ago. The state's Obamacare exchange website, Cover Oregon, has been rife with glitches and problems, leading to lower-than-expected enrollment numbers. The exchange's director announced this week he would resign in March, but not before Oregon has spent $300 million on Cover Oregon.

Furthermore, a new study of a Medicaid expansion program started in Oregon five years ago has found the expansion has increased the burden on emergency rooms rather than reduced it. That suggests Obamacare's nationwide Medcaid expansion may not reach its intended goal of clearing out crowded ERs.

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