President Joe Biden arrives back in the US this week after a foreign tour with a recurring theme: fighting climate change. But he returns to a Washington where his own party feels increasing anxiety that his administration’s climate agenda will fall short at home.

Bipartisan talks over Biden’s infrastructure proposals — which would spend billions on crumbling roads, bridges and tunnels, as well as record sums on clean energy — are flagging. While Republicans and moderate Democrats try to scale down the package, progressives warn they will withhold support if climate provisions are stripped out.

“If there is no climate, there is no deal,” Jeff Merkley, a Democratic senator from Oregon, said this week. “When the ship sails on infrastructure, energy infrastructure cannot be left on the docks.”

Democratic party leaders are now exploring another path to enact Biden’s climate plan. Chuck Schumer, the Senate majority leader, on Wednesday met his members on the budget committee to find ways to fund greener electricity, zero-carbon vehicles and manufacturing and farming that keeps many climate goals intact.

While potentially more viable, the strategy could also weaken Biden’s climate policies. Legislation would be shoehorned into the Senate’s budget reconciliation process — a special procedure that enables Democrats to use their slim majority but constrains the scope of what can pass.