House and Senate Republicans have been mostly silent about the nomination of Sylvia Mathews Burwell to succeed Kathleen Sebelius as Health and Human Services secretary, but they will likely have a lot to say when her confirmation hearings begin in May.

With Obamacare at the center of a protracted fight in Congress, Burwell, who would essentially be left in charge of the new law, is unlikely to win the same unanimous support from the Senate that she did when confirmed a year ago as the director of President Obama's Office of Management and Budget.

“This is not going to be another 96-nothing vote that she enjoyed as OMB director,” a top Republican leadership aide told the Washington Examiner. “This is going to be a fight.”

Democratic leadership aides tell the Examiner that Burwell will appear for a grilling as early as the week of May 12 before the Senate Health, Education, Labor and Pensions Committee and the Senate Finance Committee.

“She’ll be confirmed, but Republicans will use it as a chance to re-litigate Obamacare,” Brendan Daly, a former top aide to House Minority Leader Nancy Pelosi, D-Calif., told the Examiner.

If both committees approve her nomination, the full Senate will vote on whether to confirm her. Unlike past executive branch nominees who required 60 senators for confirmation, Burwell will need only 51, practically guaranteeing her ascent to Obama’s cabinet with Democrats controlling 55 votes.

But along the way, Burwell could hit some speed bumps, among them:

Vulnerable Democrats: New Senate rules allowing a simple majority to confirm Obama’s judicial and executive branch nominees mean that Burwell’s confirmation will not likely rest on whether she can win over Republicans. But Democrats control only 55 votes, which means if they lose more than five, not even a tie-breaking vote from Vice President Joe Biden can save her nomination from defeat.

It would be almost unprecedented for Democrats to turn on an Obama nominee, but this year is politically treacherous for Democrats. Eight Senate Democratic seats are either toss-ups or leaning in favor of a Republican takeover in November, and five other Democratic senators are in competitive races.

Look for tough questioning from HELP Committee member Sen. Kay Hagan, D-N.C., who has sunk in the polls in recent months due to the unpopularity of Obamacare, and Finance Committee member Sen. Mark Warner, D-Va., who is leading in the polls but in a competitive race due to the law’s low favorability.

Burwell's record as OMB director: Some Republicans were highly critical of the first and only budget Burwell presented to Congress this year on behalf of the Obama administration. It called for spending $56 billion more than the bipartisan budget agreement struck last year in Congress and signed into law.

When Senate Budget Committee Ranking Member Jeff Sessions, R-Ala., questioned Burwell about the budget-busting figure, she angered him by refusing to answer directly. Sessions believes she was stonewalling lawmakers about a plan to raise spending and taxes. Look for Republicans to try to force Burwell to provide concrete answers to difficult questions about the health care law.

She’s no expert on health care: Burwell’s resume includes a stint as president of the Walmart Foundation and head of the Global Development Program at the Bill & Melinda Gates Foundation. She’s also a member of the board of directors for MetLife. Her background is mostly business with very little expertise in health care.

“I am concerned that Director Burwell may have been chosen because the president believed her to be another political loyalist who would toe the party line,” Sessions said. “Ms. Burwell has a comparatively thin resume for the demands now placed on this position. She has never run anything on the scale of HHS.”

When Sen. Sheldon Whitehouse, D-R.I., asked Burwell last month about increasing the 2015 money-saving reforms to Medicare and Medicaid, she couldn't answer him and instead deferred to Sebelius, who served as the insurance commissioner of Kansas before becoming governor and then joining the Obama administration. “I think the question of the delivery changes that you need, and those savings and how that relates, would be something that I would consider [Sebelius] more expert than myself in terms of what kinds of impacts you would have, in terms of the delivery system, in terms of what it provides for those in the system -- individuals receiving care,” Burwell said at the March 5 hearing.

She’ll have to defend Obamacare: Burwell will have to face questioning from two committees with a combined 20 Republicans who want nothing less than a total repeal of the health care law, which has been plagued with glitches and could force millions to give up their existing insurance plans. Plus, she’ll be fielding criticism and scrutiny from Democrats like Hagan, Warner and others, who want to show constituents they are also being tough on the unpopular law.

Michael Cannon, of the libertarian CATO Institute, believes Burwell could face hard questions about how she would act on the Independent Payment Advisory Board, which is empowered with making changes to Medicare. No other members have been appointed yet due to Republican opposition, which means Burwell will be solely in charge of IPAB if changes to the entitlement are needed because of high costs. “I would think this would be the dominant theme in her confirmation battle,” Cannon told the Examiner.