Republicans are telegraphing a message to world leaders at the start of the Paris climate talks: President Obama is all alone.

To underscore that point, the U.S. House of Representatives voted on Tuesday to block regulations to rein in pollution from power plants, the cornerstone of the administration’s effort to tackle global warming.

The vote is largely symbolic, since the White House has vowed a veto that Republicans won’t be able to overturn. Yet it sends a clear signal: U.S. diplomats may be working to negotiate a global climate deal, but the president is acting without support from the majority of Congress. Conservatives aren’t missing any chance to point out that the president’s efforts to procure an agreement are far from secure.

“The next president could simply tear it up,” Senate Majority Leader Mitch McConnell proclaimed on the Senate floor on Monday, referring to the president's power plant regulations. “Governments currently engaged in this round of climate talks will want to know that there is more than just an Executive Branch in our system of government,” he added, noting that the climate agenda “may not even survive much longer anyway.”

The White House and Congress have long squabbled over the threat of climate change. Many Republicans reject the scientific consensus that global warming is real and man-made, and warn that action to cut greenhouse gases will cripple the economy. During the president’s first term, Republicans and a few Democratic defectors sunk efforts to pass climate legislation. Since then, Obama has made clear he won’t wait for Congress to take action.

Now, Republican critics are threatening to withhold funding that the president promised to set aside to help developing nations curb emissions and brace for the impact of global warming. The administration insists it will find a way to secure the funds, but as with many of the president’s climate commitments, it’s unclear if the White House can deliver on that promise.

There are indications that the rest of the world isn’t overly concerned by opposition in Congress. “Yeah, fine,” United Nations climate official Christiana Figueres reportedly said at a press conference when asked to comment on Republican attempts to undermine the president’s global-warming effort.

Still, the president’s climate agenda is unquestionably under threat. Lawsuits have taken aim at many of the environmental regulations issued by the administration. Future presidents could undermine or attempt to reverse the agenda. Congress will also continue to look for ways to thwart the president’s environmental regulations.

“We want to the world to know that there are differences of opinion between the Congress and the president on this issue and on his clean energy plan,” Republican Representative Ed Whitfield of Kentucky said on the House floor on Tuesday.

The president has waved away the idea that Republicans on Capitol Hill can derail the Paris talks. “It may be hard for Republicans to support something that I’m doing, but that’s more a matter of the games Washington plays,” he told reporters on Tuesday. “That’s why I think people should be confident that we’ll meet our commitments.”

But Obama is acutely aware of the challenge posed by global warming. The Paris talks are only a first step. Ultimately, developed nations like the United States must transition away from fossil fuels if they wish to substantially curb greenhouse gas emissions. That challenge extends long beyond the time Obama will occupy the Oval Office.

The president has dismissed the idea that America will elect a Republican president intent on tearing down his legacy. (“I’m anticipating a Democrat succeeding me,” he said Tuesday.) And Obama insists that whatever the outcome of the election, future administrations will be compelled to confront global warming, not least by the weight of international pressure.

“There’s a reason why you have the largest gathering of world leaders probably in human history here in Paris,” he said. “Everybody else is taking climate change really seriously.”