Don Berwick (J. David Ake/Associated Press)

A Harvard professor and pediatrician, Berwick never had an easy tenure in the administration. While he has won endorsements from most major medical societies, Republicans regularly attacked Berwick’s professed admiration for Britain’s National Health Service as an “example” for the United States to follow.

The resignation isn’t exactly unexpected. His recess appointment would have run up at the year. Forty-two Senate Republicans signed onto a letter, months ago, pledging to block his confirmation. In an e-mail to his staff this morning, Berwick noted that his resignation likely “does not come as a surprise to many of you.”

Berwick spent just shy of 18 months in the Obama administration. He came into office at a particularly tumultuous time, six months after the health reform law passed, and oversaw the rollout of crucial health care reform regulations, including ones that could reshape both the insurance industry as well as how Medicare pays doctors.

Many in health policy circles see him as a big thinker, the wonk who described health-care reform as having a “triple aim:” improving patient experience, improving population health and reducing costs. That concept is now ubiquitous in health policy; on a trip to Texas last week I repeatedly heard top health officials cite Berwick’s “triple aim” in explaining plans to reform the state’s Medicaid program.

What seemed to excite Berwick the most was much of his travel across the country and the various ideas he saw being tested out on the ground. “The country is abuzz with innovators, people in health care coming up with the brightest ideas, achieving innovations that lower costs,” he told me in an interview last week. Berwick may step down next week, but after serving in the administration at such a crucial time for health policy, his work will likely have an impact for years to come.

For more on Berwick’s resignation:

Republicans hail news of Berwick resignation

Obama to nominate Kaine secretary to Medicare, Medicaid post