Federal approval of a controversial gold and copper mine in Alaska that would be the largest in North America may be put on hold after a small group of influential Republicans — including the president’s son, Fox News host Tucker Carlson, a wealthy Trump donor and one of the vice president’s former top aides — launched a full-court press to block the project.

The proposed Pebble Mine was on the verge of winning a key permit from the Trump administration despite concerns from environmentalists that it could significantly damage Alaska’s world-renowned sockeye salmon fishery in nearby Bristol Bay.

That also happens to be a fishing spot of Donald Trump Jr., who made an impassioned case against the mine to his father during an early August fundraiser he hosted at his Bridgehampton, N.Y., home. Andrew Sabin, a Trump donor who was at the seaside gathering, also told the president that the mine was a bad idea. And last week, Carlson argued against the proposed mine on his television show.

This last-minute campaign by a handful of high-profile Republicans — including Vice President Pence’s former chief of staff Nick Ayers — has prompted the White House to reassess the mine, according to two individuals familiar with the matter. Both people, who spoke on the condition of anonymity in order to discuss internal deliberations, said administration officials are now weighing whether to delay granting a key permit to the mine’s sponsor, Pebble Limited Partnership.

This marks an abrupt turn of fortunes for the project and underscores the freewheeling nature of decision-making in Trump’s White House, as well as the persuasive power of the unofficial lobbying campaign, both public and private, to block the mine.

“For the three minutes, the president listened attentively to what Don Jr. was saying,” Sabin, a precious metals magnate, recalled in a phone interview. “He said he was going to look into it. ... I’ve got the feeling you’re going to see something big happen in the next 30 days on Pebble.”

The U.S. Army Corps of Engineers spent two years analyzing the operation’s potential environmental impact and concluded late last month that it would have “no measurable effect” on the area’s fish populations. That conclusion cleared the way for issuing a “record of decision” the mine needs from the federal government. That move could come as early as next week, although the Corps is still negotiating how the company will make up for the 2,200 acres of wetlands and 105 miles of streams the operation would permanently destroy.

Trout Unlimited President Chris Wood, who has worked to marshal Republican opposition to the mine, said the flurry of appeals from members of Trump’s inner circle could prove decisive. Both Trump Jr. and Carlson are members of Trout Unlimited, a nonprofit dedicated to the conservation of fish habitats, and Trump Jr. has fished in Bristol Bay several times; his brother Eric celebrated his bachelor’s party there.

“Those of who have been working on this for a long time realize this central fact, that Republicans fish, too,” Wood said in a phone interview. “I think there’s been a lot of people for years who have been quietly against the mine. We’re now in a point in the process that time is short. Either people speak up now, or we hold our tongues and there’s a massive mine in the world’s biggest salmon fishery.”

A White House spokesman declined to comment, noting that the public comment period on the permit decision was still ongoing, and deferred questions to the Army Corps of Engineers.

John P. Budnik, a public affairs specialist at the Army Corps’ Alaska district, said that while preparing the record of decision, “it is inappropriate for us to comment on opinions, to speculate on potential outcomes of our deliberations in response to media inquiries, or to answer technical questions.”

Pebble Limited Partnership CEO Tom Collier, however, said he remained optimistic the project would move forward. The firm was continuing to negotiate with the Corps over its plan to offset its environmental footprint, which he said would “far more than adequately compensate for our impact on wetlands in the region.”

“I don’t see that this issue requires presidential involvement, and I don’t see any indication that the president is getting involved,” said Collier, who served as then-Interior Secretary Bruce Babbitt’s chief of staff during the Clinton administration. “The mainstream of the Republican Party continues to support no political influence in permitting. ... I don’t see the president returning to Obama-like political influence in the permitting process.”

But the unlikely coalition fighting the mine has unleashed a fusillade to try to do just that. This summer, Ayers and Carlson found themselves cabin neighbors at a resort outside Jackson Hole, Wyo., and bonded over their shared love of the American West. When Carlson said he would be eager to help in the effort to halt the mine, Ayers suggested using his hour-long show on Fox News to make the pitch.

On Friday, Carlson aired a segment called “The Case Against Alaska’s Pebble Mine,” in which he interviewed Bass Pro Shops founder and CEO Johnny Morris. Carlson, who has voiced concern about the mine in the past, suggested that “a number of Republicans” oppose the plan and that they think: “Maybe you should do whatever you can not to despoil nature. Maybe not all environmentalism is about climate.”

Both Ayers and Trump Jr. have urged the president on Twitter to halt the project. After Jane Fonda shared a Washington Post article describing their efforts, tweeting, “I never thought I’d be in agreement with VP Pence’s former chief of staff, but I stand with @nick_ayers on this. And @DonaldJTrumpJr does too,” the president’s son responded with a joke about her activism against the Vietnam War.

“You think you’re shocked? I never thought I’d be in agreement with Hanoi Jane!” he tweeted, including a winking emoji.

Asked Wednesday about Pebble Mine, Trump Jr.'s spokesman declined to comment. Ayers also declined to comment.

The Theodore Roosevelt Conservation Partnership, a bipartisan hunting and fishing group whose CEO used to work for then-Sen. Thomas A. Daschle (D-S.D.), is running ads on Fox News and Twitter this week decrying the mine.

Sabin and Ayers, meanwhile, have made personal appeals to some of the highest-ranking members of the administration, including Trump himself, said people familiar with the discussions. Ayers has also spoken with Pence and Pence’s current chief of staff, Marc Short, among others.

Sabin, who gave $100,000 to Trump’s joint fundraising vehicle with the Republican Party in 2016, said he enlisted the help of Trump’s former top domestic policy adviser Joe Grogan, “who’s been out hunting for rattlesnakes with me.” The longtime Republican and environmental philanthropist spent 16 hours tuna fishing with Trump Jr. off Long Island earlier this month, and has met with Grogan’s successor, Brooke Rollins, as well as the president’s top domestic energy adviser, Francis Brooke.

Sabin said he has been making the business case against the project, saying it was equivalent to someone suggesting they wanted to build an 80-story skyscraper in Manhattan, and adding, “I’ve never built one g-----n brick in my life. But you know, you give me a permit, and I’ll go find someone to build it.”

“I’ve produced millions of ounces of gold, silver, platinum. I own a silver mine in Canada. In Cobalt, Ontario, I recycle precious metals. So I know the precious metals business,” he said. “How did it ever get this far?”

Earlier investors in the mine, including Anglo American and Rio Tinto, pulled out in 2013 and 2014, respectively.

Collier, whose firm is a subsidiary of the Canadian mining company Northern Dynasty Minerals Ltd., said his firm continues to be in talks with “potential new partners” about the project. “We have always anticipated adding a major mining company as an operating partner,” he said.

Once the Corps makes its final decision on the mine’s federal permit, Collier said, it “will increase the interest of those potential new partners.”

But mine opponents like Wild Salmon Center President Guido Rahr, who made contact with Ayers only recently, said federal approval is not predetermined at this point. “People having a good look before a permit is issued is important. I’m grateful that it’s getting some scrutiny,” he said.