“I don’t think Washington can fix Washington,” Dr. Coburn explains. “You’re always going to have this built-in conflict of getting re-elected. Parochial interests will trump the best interests of the nation, and the actors will do what’s expedient to be popular. It doesn’t have to be that way. There’s hundreds of thousands if not millions of people who could do these jobs well. All it requires is common sense and courage.”

Those qualities will be appreciably diminished in Washington when Dr. Coburn retires at year’s end. He is among Washington’s few true conviction politicians—unalterably against federal debt, government waste and the abuse of power. He genuinely doesn’t seem to care about being popular, or endearing himself to anyone; lately he has even grown a night-of-the-wolfman beard that is decidedly out of Beltway fashion.

Dr. Coburn was recently diagnosed with a recurrence of prostate cancer, which is why he is leaving before his term officially expires in 2016, but he still has work to do. Even if he has failed to change a political culture of self-interest and careerism, the doctor from Muskogee can still challenge his nominal party, the Republicans. This week, he and two colleagues released an ObamaCare replacement plan that offers innovative—and consequential—pro-market health-care reforms, intellectually akin to Paul Ryan’s 2011 Medicare proposal.