ONCE UPON a time, the Defense Department and the Social Security Administration reigned as the budgetary giants of the federal bureaucracy. But as health-care costs have grown and Washington has taken on more financial responsibility for them, a once-obscure civilian agency has surpassed them both: the Centers for Medicare & Medicaid Services, or CMS, which is part of the Department of Health and Human Services. In fiscal year 2011, CMS spent $962 billion on Medicare and Medicaid, about a quarter of all federal outlays that year.

A lot of that money flowed out according to established formulas and eligibility rules — that is, more or less on autopilot. Still, an agency that handles such a huge volume of taxpayer funds can never be a mere check-writing shop. It needs a steady, expert, fully empowered administrator, someone who understands both the mechanics of hospital and physician reimbursement and larger policy issues.

Yet CMS has lacked exactly that for nearly a decade. While a number of able men and women have served as temporary bosses, not one of them has had the benefit of Senate confirmation since Mark McClellan, President George W. Bush’s pick, was approved on a voice vote in 2004. (He resigned in 2006.) The problem, in a nutshell, is that the CMS directorship has gotten caught up in the polarized politics of health care. The most recent instance was the case of Donald Berwick, who served as a recess appointee of President Obama between July 2010 and December 2011 but could never overcome filibuster threats from Republicans trying to score points against Obamacare.

Now Mr. Obama has nominated the acting CMS administrator, Marilyn Tavenner, to head the agency permanently. A widely respected professional, she enjoys bipartisan support from seven past confirmed CMS administrators, as well as an endorsement from no less a conservative Republican than House Majority Leader Eric Cantor (Va.). The Senate should move expeditiously to confirm Ms. Tavenner.

More broadly, Congress should consider whether short-term political appointment remains the best way to fill this trillion-dollar post. The director of the Federal Bureau of Investigation serves a 10-year term. The commissioner of Social Security serves six years. These arrangements help minimize the politicization of functions that need to be carried out in as nonpartisan a manner as possible. Running the gigantic CMS is the same kind of job.