WASHINGTON (AP) — 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 for the program this year and 60 times larger than the $15 million Trump proposed in his budget plan just 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.