WASHINGTON — Democrats and Republicans alike raised concerns Wednesday about deep staffing cuts, funding freezes and far-reaching policy changes overseen by U.S. Health and Human Services Secretary Robert F. Kennedy Jr.

A bipartisan group of lawmakers questioned Kennedy’s approach to the job, some saying that he has jeopardized vaccine uptake, cancer research and dental health in just a few short months.

In combative and at times highly personal rejoinders, Kennedy defended the Donald Trump administration’s dramatic effort to reshape the sprawling, $1.7 trillion-a-year agency, saying it would deliver a more efficient department focused on promoting healthier lifestyles among Americans.

“There’s so much chaos and disorganization in this department,” Kennedy said Wednesday during the Senate hearing. “What we’re saying is let’s organize in a way that we can quickly adopt and deploy all these opportunities we have to really deliver high-quality health care to the American people.”

During tense exchanges, lawmakers — in back-to-back House and Senate hearings — sometimes questioned whether Kennedy was aware of his actions and the structure of his own department after he struggled to provide more details about staffing cuts.

“I have noted you’ve been unable, in most instances, to answer any specific questions related to your agency,” said Sen. Angela Alsobrooks, a Maryland Democrat.

The secretary, in turn, pushed back — saying he had not had time to answer specific questions — and at points questioning lawmakers’ own grasp of health policy.

Kennedy testified to explain his downsizing of the department — from 82,000 to 62,000 staffers — and argue on behalf of the White House’s requested budget, which includes a $500 million boost for Kennedy’s “Make America Healthy Again” initiative to promote nutrition and healthier lifestyles while making deep cuts to infectious disease prevention, medical research and maternal health programs.

He revealed that he persuaded the White House to back down from one major cut: Head Start, a federally funded preschool program for low-income families across the country.

But lawmakers described how thousands of job losses at the health department and funding freezes have impacted their districts.

One Washington state mother, Natalie, has faced delays in treatment for stage 4 cancer at the National Institutes of Health’s Clinical Center, said Democratic Sen. Patty Murray.

The clinical center is the research-only hospital commonly known as the House of Hope, but when Murray asked Kennedy to explain how many jobs have been lost there, he could not answer. The president’s budget proposes a nearly $20 billion slash from the NIH.

“You are here to defend cutting the NIH by half,” Murray said. “Do you genuinely believe that won’t result in more stories like Natalie’s?” Kennedy disputed Murray’s account.

Democrat Rep. Bonnie Watson-Coleman of New Jersey asked “why, why, why?” Kennedy would lay off nearly all the staff who oversee the Low Income Home Energy Assistance Program, which provides $4.1 billion in heating assistance to needy families. The program is slated to be eliminated from the agency’s budget.

Kennedy said that advocates warned him those cuts “will end up killing people,” but that President Donald Trump believes his energy policy will lower costs. If that doesn’t work, Kennedy said, he would restore funding for the program.

Sen. Lisa Murkowski, a Republican of Alaska, said those savings would be realized too late for people in her state.

“Right now, folks in Alaska still need those ugly generators to keep warm,” the senator said.

Murkowski was one of several Republicans who expressed concerns about Kennedy’s approach to the job throughout the hearings.