WASHINGTON >> Under fierce attack from the political right, and with even some Democrats questioning its competence, the Environmental Protection Agency is facing a tumultuous election year — with rising regulatory responsibilities, falling budgets and its very existence at stake.

The agency has long been a favorite political target for Republicans, who criticize its authority to regulate large areas of the U.S. economy as it enacts rules to curb pollution. But the EPA’s challenges in 2016 are multifaceted. The Democratic presidential candidates, Hillary Clinton and Bernie Sanders, have questioned the agency’s handling of the drinking water crisis in Flint, Mich. And a toxic wastewater spill in a Colorado river last year brought charges of incompetence from both parties.

The leading Republican presidential hopefuls, Donald J. Trump and Ted Cruz, have each vowed to eviscerate the agency.

“We are going to get rid of it in almost every form,” Trump said at a debate this month. “We’re going to have little tidbits left, but we’re going to take a tremendous amount out.”

Cruz, at the same debate, added, “I will pull back the federal regulators, the EPA and all the regulators that are killing small businesses and manufacturing.”

And House Republicans, at a hearing Thursday on the Flint water crisis, called for the EPA’s administrator to resign.

Republican policy experts are already talking about how to translate such talking points into concrete elements of the party’s policy platform, to be unveiled this summer at the Republican National Convention in Cleveland. While many policy experts are dismissive of Trump himself, the candidate’s views on a sharply limited federal role in environmental protection align with specific ideas that some conservatives have pushed for years. No matter who emerges as the Republican nominee, the party’s official policy will almost certainly take aim at the size, scope and structure of the EPA.

Conservative policymakers are considering proposals that would effectively strip the agency of its authority to set, put in place and enforce pollution standards. The agency would continue to exist, at least in name, but it could end up functioning only as a small scientific research agency, possibly swallowed into another department.

“There’s no reason to have the agency in its current form,” said Michael McKenna, a Republican energy lobbyist who has played a central role in drafting the party’s environmental policy platform in previous presidential campaigns. “Something’s going to be in the platform that gives the EPA a serious haircut.”

Democratic candidates are not exactly rushing to the agency’s defense. Clinton said that as president she would open an investigation into its handling of the Flint water crisis. Sanders said that he would “fire anybody who knew about what was happening and did not act appropriately.”

At Thursday’s hearing, Rep. Tammy Duckworth, D-Ill., a highly regarded Senate candidate, said she was “extremely troubled by how the EPA also failed in its duty to serve as the last line of defense for the children of Flint.”

The agency’s responsibilities have never been greater, and its resources have never been so strained.

Created in 1970 by President Richard M. Nixon, the EPA is charged with writing, carrying out and enforcing regulations under existing laws like the Clean Air Act and the Clean Water Act. Its rules impose restrictions on business, industry and agriculture, limiting the amount and types of pollutants that can be emitted into the air and water, as well as where and how landowners can use their property. The regulations can sometimes impose billions of dollars of costs on industry, requiring companies to install expensive pollution control technology and in some cases to shut down polluting facilities.

But President Barack Obama’s effort to combat global warming has transformed that mandate. The president’s climate policies require regulations so sweeping that the EPA has essentially been tasked with transforming major sectors of the U.S. economy, including the auto industry and the electric power sector, over the next decade.

Because those global warming regulations have been issued under the legal authority of an existing law, the Clean Air Act, it could be difficult for a Republican president to simply repeal them outright. But substantially weakening the agency that enacts the rules could effectively hamstring Obama’s climate change legacy.

Historically, environmental regulations have required polluters to install new equipment like so-called smokestack scrubbers and catalytic converters in cars, factories and power plants. But Obama’s current suite of climate change regulations, if enacted, would go far beyond that. The EPA would effectively change how automobiles are propelled (with electricity, not gasoline) and how electricity is delivered (via wind and solar, not coal), said Bob Persciacepe, the agency’s deputy administrator during Obama’s first term.

“We are at a pivotal moment in time, when, in fits and starts, the world is dealing with climate change and every country has to play an important role,” he said. “EPA has been put in the spot to do this. The weight on their shoulders is heavy.”

All of this is supposed to be accomplished under tight budgets imposed by a hostile Congress. The agency’s spending under Obama has been cut between 10 and 20 percent below the budgets of the previous three administrations, when adjusted for inflation. The agency’s budget has averaged about $8.8 billion annually under Obama, compared with (in today’s dollars) $9.7 billion under George W. Bush, $10.6 billion under Bill Clinton and $10.4 billion under George Bush. The agency’s 15,408 employees are its fewest since 1989.

As the EPA has taken on more work with fewer resources, problems have proliferated. Last year, after the EPA accidentally spilled 3 million gallons of toxic wastewater from an abandoned mine into the Animas River in Colorado, a government report found that the agency laced the technical skills to handle such tricky projects.

The agency has also been criticized for its implementation of a regulation known as “Waters of the U.S.,” which would expand pollution controls over the nation’s rivers and streams.

“It’s clear EPA cannot currently handle the issues on its plate,” Rep. Scott DesJarlais, R-Tenn., said Thursday.

A spokeswoman for the EPA declined to comment on the politics swirling around the agency. But Obama administration officials noted that the EPA still enjoyed public support. A Pew poll in September 2015 found that 52 percent of respondents had a favorable view of the agency.

That support could make it more difficult for a Republican president to enact some of the most drastic changes envisioned by those drafting the party’s policy platform because at least some proposals would have to go before Congress. And eliminating the EPA would not eliminate the government’s legal obligations to carry out regulations under existing laws.

“I’m a very conservative guy, and there are legitimate criticisms of EPA, and there has been EPA overreach,” said Jeffrey Holmstead, a former deputy administrator of the agency under George W. Bush. But, he noted, under the Clean Air Act and the Clean Water Act, the EPA is required to supply operating permits to industrial plants and manufacturers.

“Even if EPA disappeared tomorrow, the regulations would still have the force of law,” Holmstead said.

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