Sylvia Mathews Burwell was to testify Thursday before the Senate Health, Education, Labor and Pensions Committee, the first of two Senate committees that will hold hearings on her nomination.
Burwell is Obama's choice to replace Health and Human Services Secretary Kathleen Sebelius, who resigned last month after presiding over the passage of the health law and the disastrous rollout of the federal enrolmentwebsite. Sebelius left just as the law had begun to recover with stronger-than-expected sign-up numbers.
Burwell is seen as a safe pick, not least because she was unanimously confirmed by the Senate last year as Obama's budget director.
Her confirmation to the HHS post is unlikely to go so smoothly, however, even though no senator has announced opposition so far. Instead, her nomination hearings are likely to turn into a referendum on the health law itself, with Republicans viewing their opposition as a winning political issue this midterm election year, with control of the Senate at stake.
Although a closing surge of sign-ups rescued the health law's big enrolment launch from failure, Burwell faces significant challenges sustaining that momentum next year. The federal HealthCare.gov website will be called on to handle more states, with less money for consumer outreach.
Ahead of Thursday's hearing, Burwell got a boost from the health insurance industry. Karen Ignagni, head of America's Health Insurance Plans, issued a strong statement of support, calling Burwell "uniquely qualified to lead HHS during this critical time."
Burwell, a native of tiny Hinton, W.Va., was deputy chief of staff in the Clinton White House and later served as president of the Bill & Melinda Gates Foundation's Global Development Program and then the Walmart Foundation, before returning to the White House last year to run the budget office under Obama.
If confirmed, she will preside over a $1 trillion bureaucracy that rivals the Pentagon in complexity.
The Health Committee won't actually vote on Burwell's nomination; that task falls to the Senate Finance Committee, which has yet to schedule its hearing.
Associated Press writer Ricardo Alonso-Zaldivar contributed to this report.