Relief and satisfaction in climate action circles over an agreement to phase out the use of hydrofluorocarbons (HFCs) may be premature, U.S. legal experts warn, since the deal may not find the two-thirds support its ratification will require from a United States Senate dominated by Republicans hostile to environmental regulation.

Reached last week by almost 200 countries, the Kigali Amendment to the 1987 Montreal Protocol on chlorofluorocarbons would begin a phased drawdown of HFCs over nine years beginning in 2019. Without that action, HFCs in the atmosphere were on track to add another 0.5°C to average global warming.

But under U.S. law, confirming American endorsement of the amendment “would almost certainly require a two-thirds vote from the Senate,” The Guardian writes.

“This is different from Paris, in that it requires ratification,” Stanford environmental law specialist Michael Wara told the paper. “This is going to require getting Republicans to vote for it.”

Republicans now control the U.S. Senate, and while some observers speculate that the candidacy of reality TV star Donald J. Trump may hand the Democrats a simple majority in the upper chamber, its losses are unlikely to put two-thirds of the body in Democratic hands.

And Republican Congressional losses are by no means certain. The subscription-only Energy and Environment News reports that “oil and gas executives are pouring record amounts of money into electing Republicans this year, even though they’re largely sitting on their wallets in the presidential race.

“Although Trump offers kind words, the industry’s politically active members figure he can’t win,” the specialty outlet reports. “So instead, they’re pouring their money into the Republican effort to keep control of Congress.”

According to OpenSecrets.org, contributions to Republican candidates from oil and gas industry sources are 50% higher than in the last general election cycle 2012.