Just five years ago, the Environmental Protection Agency determined that a proposal to dig a massive open-pit copper and gold mine near southwest Alaska’s Bristol Bay — one of the world’s most important salmon fisheries — threatened an environmental disaster. So it issued rules to severely curtail the potential project.

What a difference an election makes.

Shortly after President Donald Trump’s appointee, Scott Pruitt, took over the EPA in 2017, he met with the chief executive of Pebble Limited Partnership, owned by Canada-based Northern Dynasty Minerals, and then just hours later rescinded the Obama administration directive to protect the sensitive wetland area from mining activities. Pruitt later backed off and sent the action for a fuller regulatory review — and then quit his job under a storm of criticism about ethical lapses.

But the EPA has continued Pruitt’s campaign to loosen environmental restrictions and greenlight controversial projects, and on Tuesday the agency announced that it would not use its veto authority under the Clean Water Act to block the mine. That frees the Army Corps of Engineers to decide whether or not to approve the project.

Environmentalists, including Natural Resources Defense Council attorney Joel Reynolds, accuse the EPA of abandoning its own findings and opening the door for the Trump administration to deliver a “gift to a foreign mining corporation at the expense of Bristol Bay’s fish, aquatic resources and community.” We would add that the EPA has also abandoned common sense.

Mining is an exceedingly messy endeavor that historically has ravaged landscapes and caused significant environmental degradation — just the kind of thing the federal government’s environmental watchdogs are supposed to protect against. The EPA’s absurd decision to reverse itself and let the Pebble Mine permitting process proceed must be undone either through an unlikely reconsideration by the EPA, legal challenges or, best yet, rejecting Trump and his cockamamie and dangerous approaches to economic development in the 2020 election.

What’s at stake in Alaska? The proposal is for an open-pit mine and support operations with a potential footprint as large as Manhattan, and a pit descending nearly three-quarters as deep as the Grand Canyon, according to an EPA analysis (which the developers have disputed). Even if it were only half that size, that is an extraordinary amount of environmental degradation at the mine site itself, which would include massive pits to hold millions of tons of mine waste and other leftovers of the mining process — much of it laden with toxic chemicals.

And the site is near two rivers that empty into Bristol Bay, which means that not only would the project destroy thousands of acres of near-pristine habitat and wetlands at the mining site, but it would also imperil the environmental health of Bristol Bay itself — something the Obama EPA recognized. As have the people of Alaska: 65% approved a measure in 2014 that gives the state Legislature veto power over future projects in the Bristol Bay watershed if it determines that the salmon fishery is at risk, a veto it ought to keep handy should federal regulators allow this mine to proceed.