WASHINGTON  — Senate leaders and the Trump administration have reached an election-year deal to double spending on a popular conservation program and devote more than a $1 billion a year to clear a growing maintenance backlog at national parks.

The deal, announced Wednesday by senators from both parties, would spend about $2.2 billion per year on conservation and outdoor recreation projects and park maintenance across the country.

If approved by Congress and signed by President Donald Trump, the bill “will be the most significant conservation legislation enacted by Congress in nearly half a century,″ said veteran Sen. Lamar Alexander, R-Tenn.

Alexander was one of 12 senators from both parties who hailed the bill at a news conference Wednesday. The breakthrough, which is supported by the leaders of both parties, came as Trump tweeted support for the proposal despite repeatedly trying to slash spending for the federal Land and Water Conservation Fund in recent years.

The program uses federal royalties from offshore oil and gas drilling to pay for conservation and public recreation projects around the country. The 55-year-old-fund is authorized to collect $900 million a year but generally receives less than half that amount from Congress.

The plan announced Wednesday would fully fund the conservation program and add $1.3 billion a year for deferred park maintenance. The proposed $900 million for land and water conservation is nearly double the $485 million Congress approved this year and 60 times larger than the $15 million Trump proposed in his 2021 budget last month.

Trump credited Republican Sens. Cory Gardner of Colorado and Steve Daines of Montana for his change of heart. “ALL thanks to @SenCoryGardner and @SteveDaines, two GREAT Conservative Leaders!″ Trump tweeted.

Both Daines and Gardner are seeking reelection this year, and Gardner is considered one of the Senate’s most vulnerable incumbents. Gardner, who went to the White House with Daines last week to lobby Trump on the bill, denied that politics played a role in the president’s reversal. He and Daines said they showed Trump pictures and maps of their states and stressed the importance of conservation in the West. They also noted that Senate Majority Leader Mitch McConnell backs the bill.

“I’m not going to try to play politics or point partisan fingers,″ Gardner told reporters Wednesday. “I’m going to focus on the good the great outdoors does.″

Sen. Joe Manchin, D-W.Va., said he didn’t care about the plan’s politics, only that it helped his state and others across the country. “Politics be dammed, let’s get this done,″ Manchin said, standing next to Gardner at a Capitol news conference.

Daines also downplayed the bill’s politics, saying, “This is a bipartisan moment.″

“This is about doing the right thing for America,″ added Sen. Tom Udall, D-N.M.

Former Colorado Gov. John Hickenlooper, the Democratic front-runner to challenge Gardner, said in a tweet that Gardner supported cuts to the conservation fund as recently as 2018. Gardner also voted to confirm former oil and coal lobbyist David Bernhardt as interior secretary.

“Only President Trump would praise a record like this,″ Hickenlooper said.

Trump predicted Congress will approve the plan, which helps address a $12 billion backlog in maintenance of national parks. “When I sign it into law, it will be HISTORIC for our beautiful public lands,″ Trump said in a tweet.

Sen. Jon Tester, D-Mont., called Trump’s tweet “good news,″ but added, ”It’s almost too good to be true.″

At a budget hearing Wednesday, Bernhardt joked that Trump’s tweet caused “heart palpitations” at the White House budget office, but said he and the rest of Trump’s administration support full funding for the conservation program and for clearing the maintenance backlog, a longtime priority of interior secretaries of both parties.

“The president made his comment and I’m pretty 100% confident everybody’s getting in line,″ Bernhardt said. He called the proposal ”a tremendous opportunity for conservation in America” and urged Congress to “seize the day.″

Udall praised Trump’s political instincts, saying, “the president was right to sense that this is a popular issue.″ A recent poll found that 70% of Westerners, including majorities of both parties, support full funding of the conservation program.

“If the president is sincere in abandoning his administration’s previous attempts to gut” the fund, he and other Democrats are eager to work across party lines ”to get this done for the American people and for future generations,” Udall said.

Sen. Maria Cantwell , D-Wash., called the Land and Water Conservation Fund the nation’s most successful conservation program.

The late Washington Sen. Henry “Scoop” Jackson helped create the program in the mid-1960′s, “but over the years it has been shortchanged by more than $20 billion,″ Cantwell said. ”That’s why I am so grateful that our years of effort to get full and permanent funding for LWCF now has the bipartisan support we need to make it the law of the land.″

At the same time, the bill will address an “unacceptable” maintenance backlog at national parks like Olympic and Mount Rainier in her state, Cantwell said. “Passing this legislation will be a huge boost for the outdoor recreation economy,” she said.

Bills to boost the conservation fund and address the maintenance backlog have bipartisan support in the Democratic-controlled House.