The Obama administration will leave behind a host of disputed recent actions and unfinished business on the environment - from shelved energy leases and blocked mining projects to pollution restrictions and decisions on hundreds of potentially imperiled species.
Republicans and business groups emboldened by Donald Trump's victory are gearing up to reverse many of the administration's signature environmental moves, particularly those made since the election.
The outcome could determine whether eight years of Democratic rule in the White House leaves a lasting mark on the environment or quickly fades.
Already environmental groups and their Democratic allies are raising alarms over Trump's choice of Oklahoma Attorney General Scott Pruitt to head the Environmental Protection Agency and Texas Gov. Rick Perry for Energy Secretary, and the emergence on Tuesday of Montana Rep. Ryan Zinke as his choice for Interior Secretary. All three are industry proponents who have lined up against Obama on environmental issues and expressed doubts about the science behind climate change.
"Obama may be in danger of losing his entire legacy," said Rep. Rob Bishop, chairman of the House Natural Resources Committee, who pointed to "excessive" administration moves on the environment that attracted a Republican backlash.
"From the top, the president (Trump) on down, there is a commitment to making change, and the stars are aligning to see that change take place," the Utah Republican said.
Reversing course from the Obama years could happen with the stroke of a pen for a moratorium on new coal sales and recent mining claim withdrawals in Montana, Oregon and Washington. Trump already has said he would knock down the coal moratorium.
Other administration actions will be harder to unravel, legal and industry experts said. Those include blocked oil leases in the Arctic and limitations on methane emissions to reduce greenhouse gases from the oil and gas industry, which would require congressional action or the reopening of lengthy bureaucratic processes.
Yet with the GOP in firm control of Congress, the White House and likely the Supreme Court, "they are going to have an easier time getting their way" on environmental issues, said Mark Squillace, a professor of natural resource law at the University of Colorado.
"It is easier to break things than it is to create them. ... On some level, Trump wants to come in and break things Obama has created," he said.
The Obama administration's scramble to finalize key environmental policies in its last days obscures the fact that many of those actions were in the works for years. Nevertheless, the industry wish list for Trump and the next Congress has grown with each recent announcement.
Senior administration officials reject allegations that they're ignoring public sentiment in the rush to get disputed and controversial items over the finish line before their power expires.
As evidence, officials pointed to the yearslong process that resulted in the methane rule and the millions of public comments received prior to shelving future energy lease sales in the Arctic.
It would not make sense for that work to "just be put in a drawer" because of the election, Bureau of Land Management Deputy Director Linda Lance argued.
"There are good moderate proposals that have very much taken into account the concerns of the public. We would hope the work that's done will be respected and continue," she said.
Among the most powerful legislative instruments Republicans promise to wield to overturn recent moves by the current administration is the Congressional Review Act. The 1996 law, passed as part of then-Speaker Newt Gingrich's "Contract with America," allows lawmakers to overturn rules recently issued by a previous president.
It would apply to rules submitted since May 30, the nonpartisan Congressional Research Service has said. It's been used successfully only once, to kill a 2000 rule on workplace ergonomics from the Clinton administration.
Prominent Republicans including Sen. John Barrasso of Wyoming promised to use the law when the administration last month finalized the methane rule, which would restrict companies from burning off excess natural gas, a contributor to climate change. Barrasso chairs the Senate Subcommittee on Energy and Natural Resources.
He said the rule would drive oil and natural gas companies off public lands and showed the Obama administration was "unwilling to listen to the message that the American people sent" with Trump's election.
Meanwhile, conservation groups that frequently prodded the Obama administration to be more aggressive on the environment now find themselves at risk of being marginalized.
In recent years those groups complained that timelines for greenhouse gas reductions were too long. They accused the administration of underfunding agencies that oversee endangered species protections. And they went to court to challenge sales of federally owned coal with no regard for future pollution.
Activists acknowledged they will soon need to shift their focus to the Republicans, who they predict will open more public lands to oil and gas drilling, mining and logging and will attempt to dismantle the Endangered Species Act.
"We have to play defense now, and that's what we're going to do. We're expecting full-on trench warfare," said Jeremy Nichols, climate program director for the nonprofit environmental group WildEarth Guardians.