The administration has not disclosed the exact timing or content of its revised water rule, but the version it proposed in 2018 would — according to the agency’s ownanalyses — remove environmental protections for roughly half the country’s wetlands and millions of miles of streams. Those include the vast majority of waterways in arid states like Arizona and Nevada.

The final rule would replace a much further-reaching Obama-era regulation, known as the Waters of the U.S. rule, that had drawn opposition from GOP-aligned industry groups before the Trump administration repealed it last year. The new rule represents Trump’s second major effort to hobble the country’s foundational environmental laws in as many weeks — showing that even a president about to face a Senate impeachment trial has the power to push a deregulatory agenda that could have lasting environmental and economic consequences.

The rewrite comes over the objections of the EPA’s own scientific advisers — mostly Trump administration appointees — who said last month that the proposed rule is “in conflict with established science … and the objectives of the Clean Water Act.”

But the new rule would fulfill a 2016 campaign promise from the president, and it is getting vocal cheers from the agriculture industry, which fought bitterly against the now-repealed Obama rule.

“It was the largest federal land grab of our farms and our lands and taking our private property rights in the history of our country, and this organization showed its strength by making a move to try to do away with that rule and get a new one,” Farm Bureau President Zippy Duvall said during his keynote address at the organization’s annual meeting last year.

Limiting the scope of the 48-year-old Clean Water Act, the country’s foremost water law, has been a long-time priority for other industry sectors as well, including homebuilding, oil and gas production and mining. While the administration has not yet released the final text of its rule, environmentalists say the version it proposed in 2018 would gut the landmark law.

“There is a value in having uniform federal protections for the nation’s waters,” said Jon Devine, a longtime water attorney for the Natural Resources Defense Council. “It protects downstream states from pollution upstream. It ensures that industries don’t seek out states that have weaker pollution controls. It ensures that there are sufficient resources to implement the law.”

The Trump administration argues that the federal government has long overstepped its authority under the Clean Water Act, and that a narrower definition would allow states to enact the protections better suited to their waterways.

The new rule is expected to enshrine a definition of protected waterways that is far narrower than both the Obama rule and a previous, long-standing definition that the Supreme Court threw into question in a 2006 decision. Legal experts say the question of which streams and wetlands are protected under the Clean Water Act is unlikely to be answered until the Supreme Court rules again, and many see the Trump administration’s new rule as crafted with the primary goal of winning over five justices.

While the 2018 rule proposal would represent the greatest retraction of federal protections since the Clean Water Act was passed in 1972, the Trump administration could roll it back even further in the final version. In addition to proposing that waterways that flow only after rainfall lose federal protection, the administration also left open the possibility that it could remove protections for seasonal streams, which are crucial to many ecosystems and water supplies, especially in the West.

Environmental groups will also look closely at how the administration explains the impact that exempting large swaths of the nation’s waters from pollution limits and penalties will have on the nation’s water quality, something they say the administration sidestepped when it proposed the rule.

Regardless of the details, the new rule is expected to offer an important political victory for farmers, who overwhelmingly supported Trump in 2016 and have largely stuck by him during his presidency despite suffering financially from the fallout of his trade wars, immigration crackdown and biofuels policy.

The Farm Bureau led opposition to the Obama-era rule, which cemented federal protections for millions of miles of small streams and wetlands. The bureau launched a campaign to “Ditch the rule” — a nod to the group’s complaints that even dry ditches could fall under federal authority. The effort included yard signs, community meetings and even a spoof music video starring a farmer’s wife crooning about government overreach from the banks of an empty ditch as her family attempts to swim in it

A partial U.S.-China trade deal that is expected to cover American farm exports, as well as a new North American trade agreement that Congress is set to pass this week, could ease some of farmers’ strife, which has included plummeting prices for milk and other commodities, mounting debt and a wave of farmer suicides. (Rollbacks of regulations like the water rule will likely have little direct effect on their bottom lines — farming is almost entirely exempt from the Clean Water Act’s permitting requirements.) However, a December poll of 400 agricultural producers across the country by Purdue University and the CME Group found that confidence in economic conditions was actually trending down.

The Obama-era water rule was one of Trump’s top targets for rollback on the campaign trail in 2016. He signed an executive order barely a month after taking office that called for his administration to launch the process for a repeal and replacement.

EPA finished the rule repealing the Obama version in September, and is already facing court challenges from environmental groups, Democratic states and even conservative property rights activists. The new replacement rule is also expected to face a slew of court challenges once completed, adding to the tangled web of litigation that has developed around the scope of the Clean Water Act over the past decade.

Until the Trump administration repealed the Obama-era rule last fall, the country faced a regulatory patchwork, with 22 states bound by that 2015 rule and 28 covered by court injunctions that put the previous rule back on the books. Legal experts say the Trump administration’s rule is apt to lead to similar results, creating uncertainty for years to come.

Catherine Boudreau contributed to this report.