If there’s anything sacrosanct among congressional Republicans, it’s opposition to taxes and climate change action. Now that front is cracking, barely. Fissures are showing up first in US congressional districts held by Republicans, but won by Democrat Hillary Clinton in 2016.

Divisions were laid bare this week when Republican representative Carlos Curbelo of Florida announced (paywall) a bill to cut the federal gasoline tax, and impose a new tax on carbon emissions. Revenue would fund low-income housing, coastal flooding relief, renewable energy and aid displaced coal workers. The “Market Choice Act,” the first GOP proposal to put a price on carbon in about a decade, won over the libertarian think tank Niskanen Center and The Nature Conservancy, but failed to impress many Republican colleagues. Just days earlier, all but seven of 236 House Republicans voted for a non-binding resolution calling a carbon tax “detrimental to American families and businesses, and is not in the best interest of the United States.”(Six voted against the resolution, and one voted present.)

Yet Curbelo is not alone in his climate efforts. Calls by pragmatic moderates and younger Republican voters to take action on climate are now too hard for some in the GOP to ignore. That pressure has been most intense on Republicans in districts won by Clinton in the 2016. Data collected by Ballotopedia show that 60% of Republican officials in congressional districts carried by Clinton have broken with party orthodoxy to join the bipartisan Climate Solutions Caucus. Founded by Curbelo and Florida Democrat Ted Deutch, the group is dedicated to pushing economic measures to slow global warming. It claims 43 Democrats, and 43 Republicans, 15 of whom are in congressional districts won by Clinton in 2016 (see list below).

GOP member District Steve Knight (CA-25) Ryan Costello (PA-06) Peter Roskam (IL-06) Mimi Walters (CA-45) Mike Coffman (CO-06) Leonard Lance (NJ-07) Kevin Yoder (KS-03) Ileana Ros-Lehtinen (FL-27) Erik Paulsen (MN-03) Ed Royce (CA-39) David Reichert (WA-08) Darrell Issa (CA-49) Carlos Curbelo (FL-26) Brian Fitzpatrick (PA-08) Barbara Comstock (VA-10)

But the prospect for swift action on a carbon tax remains remote despite being one of the economically efficient ways of reducing emissions. A study by Columbia University found Curbelo’s proposal would have almost no effect on economic growth, reducing annual gross domestic product by less than 0.2%.

For now, most GOP members remain committed the status quo. Even the majority of Republicans in the Climate Solutions Caucus, which some have called a fig-leaf for Republicans unwilling to take meaningful climate action, voted to condemn a carbon tax in last week’s House resolution. Curbelo said he had more GOP support for his bill, but declined to name specific backers. But that’s progress, Mark Reynolds of the Citizens’ Climate Lobby told The Washington Post (paywall). In previous congresses, every member of the GOP member voted to condemn a carbon tax.