Republicans are getting their chance to ply the top official implementing President Obama's healthcare law with questions just days after the third enrollment season came to a close.

Health and Human Services Secretary Sylvia Mathews Burwell testified before the House Ways and Means Committee on Wednesday, and on Thursday she is scheduled to appear before the Senate Finance Committee. Both hearings are technically about Obama's proposed budget, but they mostly represent a chance for lawmakers to ask Burwell whatever they want.

Unlike in years past, when GOP complaints about the Affordable Care Act have centered on its initially disastrous website or the administration's decisions to delay some of its mandates, lawmakers so far have presented a variety of concerns this week about the sweeping legislation.

House Ways and Means Committee Chairman Kevin Brady kicked things off by grilling Burwell about why enrollment came in lower than nonpartisan analysts projected. Burwell acknowledged that's the case, but argued that it's partially because fewer people than expected switched from employer-sponsored coverage to the Obamacare marketplaces.

Brady also pressed Burwell over a question that Republicans are suing HHS over — whether it's legal for the administration to fund subsidies to help the low-income afford copays and other cost-sharing features, as the GOP-led Congress has refused to allocate that money.

Last fall, a federal judge in the District of Columbia ruled the lawsuit can go forward, after the administration had asked for it to be dismissed.

Brady is separately seeking documents from HHS explaining where the funding originated. "This administration paid out more than $5 billion for these payments in clear disregard of the law," he told Burwell.

"We believe the authority exists," Burwell responded, naming a specific U.S. code.

Other Republicans asked questions about why about half the law's nonprofit health insurance cooperatives have failed, why Obamacare puts more limits on how tax-free health savings accounts can be used and whether HHS is taking steps to guard against subsidy overpayments in the marketplaces.

And some Republicans, such as Rep. Todd Young of Indiana, just wanted to air general discontent with the law.

"Deductibles are skyrocketing, premiums are going up," Young told Burwell. "I start to glaze over when I talk to my constituents about all the specific numbers. It doesn't seem like we have a functioning system."

Burwell defended the law, noting its more popular provisions such as banning insurers from discriminating against people based on pre-existing health conditions.

"I don't think most people in the U.S. want to go back to a place where pre-existing conditions keep you off healthcare," she said.

Burwell, who has served as HHS secretary for nearly two years, faced a tough task in presiding over Obamacare's third year of enrollment. While the federal marketplace, healthcare.gov, is working much better than in years past, the administration faced an uphill battle in expanding the number of enrollees.

While about 12.7 million people have selected marketplace plans, that number is expected to drop during the year. It's already below enrollment projections by the Congressional Budget Office and some independent analysts.

Republicans have fought the law in the six years since it was passed, and that's what Democrats took aim at Wednesday, with ranking member Sander Levin, D-Mich., criticizing his GOP colleagues for repeatedly trying to repeal it.

"You'll hear a lot of that ideology today ... but I think the realities are so different from that ideology," Levin said.

And they also peppered Burwell with their own pressing healthcare questions, like what Obama is doing to combat the problem of rising drug costs.

"I want to ask you about drug costs, because drug costs are scaring the living daylights out of people," said Rep. Jim McDermott, D-Wash.

Burwell pointed to three measures in the fiscal 2017 budget proposal the White House rolled out Tuesday.

The document proposes to allow Medicare to negotiate lower prices with drug makers, create a federal-state negotiating pool for high-cost Medicaid drugs and speed up the closure of Medicare's so-called "doughnut hole" in which seniors have to pay for their drugs.