WASHINGTON >> President Barack Obama has one hand tied behind his back as he heads to Paris on Sunday to try to negotiate a legacy-making climate change pact.

Congress can’t even agree whether global warming is real.

Scientists point to the global agreement as the last, best chance to avoid the worst effects of global warming. Obama has prodded other countries to make ambitious carbon-cutting pledges. He hopes the deal will become the framework to tackle climate change long into the future.

But Republicans have tried to undermine Obama by sowing uncertainty about whether the U.S. will ever make good on its own contribution.

Senate Republican leader Mitch McConnell and others have warned other countries not to trust any deal from Obama. Meantime, their allies are working to nullify Obama’s emissions-cutting steps.