Sylvia Mathews Burwell defended the Affordable Care Act, asserting that it has improved the economy, held down the growth of health costs, reduced premiums and expanded coverage.
The law "is making a positive difference in the lives of our families and our communities," Burwell, who now serves as Obama's budget director, said in testimony before the Senate Health, Education, Labor and Pensions Committee, the first of two Senate committees that will hold hearings on her nomination to lead the Health and Human Services Department.
Republican senators disagreed. The top committee Republican, Sen. Lamar Alexander of Tennessee, warned her that Republicans hope to retake the Senate in November and scale back the law in numerous ways.
"Republicans would like to repair the damage Obamacare has done," Alexander said.
But at the same time, Alexander cited Burwell's "reputation for competence," and she was effusively introduced at the hearing by another Republican, Sen. John McCain of Arizona. Sen. Richard Burr, R-N.C., declared he plans to vote in favor of her nomination, calling her a "tremendous asset."
The exchanges point to a smooth confirmation for Burwell, 48, even as her nomination hearings allow Republicans to focus renewed election-year attention on the unpopular health law.
Republicans stacked a large pile of documents behind the dais wrapped up in red tape and labeled "Obamacare Regulations," and prodded Burwell on controversial aspects of the law, asking if she aimed to turn it into a fully government-run system like Medicare — Burwell indicated she did not — or to change any more of its requirements.
"What we are trying to do is commonsense implementation within the law. That is the objective," Burwell replied.
Burwell was confirmed as budget director last year on a 96-0 vote, and no senator has announced opposition so far to her nomination to the HHS post.
She is Obama's choice to replace HHS Secretary Kathleen Sebelius, who resigned last month after presiding over passage of the health law and the disastrous rollout of the federal enrollment website. Sebelius announced her departure just as the law had begun to recover with stronger-than-expected sign-up numbers.
Burwell faces significant challenges in sustaining that momentum next year. The federal HealthCare.gov website will be called on to handle more states with less money for consumer outreach.
And as the law's second open enrollment period approaches in November, Burwell has little control over the main factor affecting sign-ups: potential premium increases by insurers.
Burwell can claim the support of the health insurance industry. Karen Ignagni, head of America's Health Insurance Plans, called her "uniquely qualified to lead HHS during this critical time."
A native of tiny Hinton, W.Va., Burwell 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 of the Wal-Mart 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, with responsibility for the Food and Drug Administration and the Centers for Disease Control and Prevention, as well as research under the National Institutes of Health and the Medicare and Medicaid programs for the elderly, poor and disabled.
The health committee won't actually vote on Burwell's nomination; that task falls to the Senate Finance Committee, which is expected to hold a hearing in coming weeks. A floor vote in the full Senate could happen as early as this month.
Associated Press writer Ricardo Alonso-Zaldivar contributed to this report.