WASHINGTON – A rollback of mercury emissions standards. A revamp of clean water regulations. A retreat from a climate change agenda.

Democrats have seethed as they helplessly watched the Trump administration undo or block a slew of Obama-era environmental proposals during the past two years.

On Wednesday, they got a chance to grill President Donald Trump's point person on deregulation as Andrew Wheeler came to Capitol Hill for his confirmation hearing to be the next permanent administrator of the Environmental Protection Agency.

The reception he got before the Senate Environment and Public Works Committee was predictably rough from Democrats who scolded him for working to undo the many Obama-era rules they believe have made the air, water and land safer for Americans.

"It remains my hope that you can reverse course and commit to seize upon (policies) that protect our environment while providing industry with certainty which they deserve," Delaware Sen. Tom Carper, the top Democrat on the panel told Wheeler. "That is what the American people expect and deserve from anyone who’s been nominated to lead the Environmental Protection Agency. Based on what we’ve seen so far, without such commitments, that is not the nominee that we have before us today."

Wheeler, who took over as acting EPA chief after Scott Pruitt left in July under an ethics cloud, is expected to win confirmation in the Republican-controlled Senate. But the hearing gave Democrats a public platform to vent about a president – and an agenda – they consider dangerous to the health of citizens and the planet.

At the hearing, Wheeler mentioned the agency's work cleaning up 22 toxic sites last year that have languished for decades on the federal Superfund list, the emphasis on lead removal from drinking water, and a proposal announced in November to reduce nitrogen oxide (NOx) emissions from heavy-duty trucks, which he noted was not required by law or court order "but makes sense to do."

All of these "reforms," he told senators, are being done to provide "regulatory certainty" to states, industry and other stakeholders.

"The Trump administration is proving that burdensome federal regulations are not necessary to drive environmental progress," he said. "What make our actions effective and durable is our commitment to vigorously enforce them."

Democrats leveled their harshest criticism against the acting administrator on the subject of climate change.

A federal report released in November, which included research from 13 government agencies including the EPA, concluded that global warming is accelerating and that a dramatic response to reduce carbon emissions is necessary.

Wheeler said climate change was an "8 or 9" on a scale of 1 to 10 in terms of its importance and called it a "huge issue," though not a crisis.

And when Sen. Bernie Sanders, I-Vt., pressed him on whether he agreed with Trump's earlier characterization that global warming is a "hoax," Wheeler deftly sidestepped: "I have not used the hoax word myself."

But when asked whether he agreed with the conclusions of the Fourth National Climate Assessment, Wheeler said he couldn't answer because he had not been fully briefed on the report.

"That's unacceptable," Sen. Ed Markey, D-Mass., told him. "You're looking to be confirmed as the head of the Environmental Protection Agency. We're having a hearing on your worthiness for this job and you very conveniently haven't had enough time yet to review whether or not there's an extra level of urgency to this problem."

Wheeler barely began his remarks when protesters in the room interrupted him. Even after they were escorted out, disruptive chants against him could be heard outside the hearing room as he continued speaking.

Wheeler, 54, a former EPA bureaucrat, Capitol Hill aide and energy lobbyist known for his low-key demeanor, has been the agency's acting administrator since Pruitt left in July.

Wheeler has the backing of a key Republican: Environment and Public Works Committee Chairman John Barrasso, R-Wyo., who encouraged Trump to nominate him months ago.

“We know how well qualified Mr. Wheeler is, and when confirmed, what a wealth of experience and expertise he’s going to bring to this critically important job," Barrasso said at the start of Wednesday's hearing.

Over the past several months, Wheeler has taken a few steps that pleased some Democrats and environmentalists.

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As soon as he took over as acting administrator, Wheeler tried to reassure EPA employees who may have felt marginalized under Pruitt that he respected their work. He reversed a Pruitt proposal to undo an Obama-era cap on the sale of heavy-duty vehicles known as “glider trucks." And earlier this month, the EPA told lawmakers it will abandon efforts to roll back an Obama-era rule prohibiting anyone under 18 from handling restricted-use pesticides.

But environmental and public health advocates mainly regard Wheeler as a shrewder and less ethically scarred version of Pruitt.

Shortly after taking over in July, Wheeler's EPA moved ahead with a plan to do away with the Obama-era Clean Power Plan and replace it with a proposed rule to set state guidelines for power-plant emissions of greenhouse gases that contribute to a warming planet. And his agency finalized revisions to a 2015 Obama-era rule regulating the disposal of coal ash that gives states and utilities what he called "much needed flexibility" to manage their waste.

He also recommended freezing miles-per-gallon standards for cars and light trucks after the 2020 model year and preventing California and other states from setting tougher standards, saying it will improve safety and keep prices lower for consumers.

"We haven't slowed down and we haven't missed a step," Wheeler in August told the same Senate committee that held his confirmation hearing Wednesday. "As you can see, we're continuing the president's agenda post-haste."

But few steps have alarmed activists more than the EPA's proposal last month to roll back mercury emission standards applied to power plants by significantly devaluing the health benefits that justified the current rule. Critics, including Carper, say the move could be used to weaken a raft of other federal environmental regulations that Trump wants to eliminate.

Harold P. Wimmer, president and CEO of the American Lung Association, recently called EPA's mercury proposal "one of its most dangerous efforts yet."

While Wheeler's confirmation appears imminent in the coming weeks, Carper said in an interview last week that there's no guarantee.

That's because the House, now controlled by Democrats, is planning hearings on the Trump administration's environmental agenda that could unearth troubling findings which might convince enough Republicans to oppose Wheeler, the senator said.

"They have the ability to subpoena. They have the power to do investigations," Carper said of the House committees. "My guess is they're going to be focused on this intently even though they're not part of the confirmation process. You never know what's going to come out of that oversight."