And who will replace Burwell?

Kathleen Sebelius, the public face of the botched rollout of the HealthCare.gov website, is resigning from her post as secretary of the Department of Health and Human Services. Sylvia Burwell, director of the Office of Management and Budget, has been tapped to take over.

The move comes as the Obama administration is taking something of a victory lap for steering a reported 7.5 million people to private health plans under the Affordable Care Act -- slightly up from Congressional Budget Office projections and by all accounts more than was expected after the site's disastrous October launch.

The "tech surge" that fixed the site was managed by former White House official Jeff Zients and took place largely out of public view. Sebelius occupied the spotlight, taking responsibility for HealthCare.gov's problems and appearing before Congress in a series of bruising hearings that revealed there was not much in the way of hands-on executive oversight by HHS of the design, build, and testing of the site.

By contrast, Burwell's relations with Congress appear to be excellent. Not only was she confirmed by a 96-0 vote, but the Clinton administration veteran and former WalMart Foundation executive has established herself as a reliable partner for appropriators and oversight committees. Members of Congress are important OMB customers, and from a recent hearing of the Appropriations subcommittee that funds the agency, it's clear that members on both sides are pleased with Burwell's openness, availability and responsiveness.

An unnamed White House official touted her role in passing the recent two-year budget deal, telling Politico, "She navigated a lengthy shutdown. She has proved to the president and everyone around here that she is a masterful manager and someone who can really run a process and dig in and figure things out. And she’s very well liked on the Hill."

Burwell's Senate confirmation hearing likely will be consumed by the politics of the Affordable Care Act, especially with the 2014 midterm elections looming. Sen. Orrin Hatch (R-Utah), the ranking member on the Senate Finance Committee that will vet the nomination, is a determined opponent of the legislation, as are all the Republican members of the panel. But it's hard to think of another high-ranking Obama administration official with as smooth a path to confirmation as Burwell, and Senate rules make it next to impossible for Republicans to fully block the nomination.

There is not yet a clear candidate to fill Burwell's slot at OMB. Brian Deese, the Deputy Director on the budget side, has been an influential economic policy voice in the Obama White House, but he is in his mid-30s and may not be considered seasoned enough for the job. Deputy Director for Management Beth Cobert is another possibility, although she was sworn in only last October, and is in the midst of implementing the Obama administration's management agenda. And Zients, now a White House economic advisor, twice held the top OMB post on an acting basis and is another possible candidate.