President Donald Trump's decision to withdraw from the Paris Agreement is a heavy blow to a deal that in many ways was designed to ensure the participation of the United States, regardless of whether Democrats or Republicans control the White House.
The U.S. under the Obama administration played a leading role in making the deal come together and convincing China and other developing countries that they needed to join the fight against global warming.
In difficult talks leading up to the December 2015 accord, other countries often yielded to U.S. positions so that the world's biggest economy wouldn't walk away, as it did from the previous climate deal, the Kyoto Protocol.
Most importantly, developing nations abandoned their long-held notion that reducing greenhouse gas emissions was an obligation just for rich countries - the main reason that the George W. Bush administration refused to join the Kyoto deal. The Paris Agreement applies to both rich and poor countries, though it says the rich should take the lead in cutting emissions.
The deal's transparency rules also reflect U.S. priorities, as countries including China, the world's biggest carbon polluter, grudgingly agreed to open up their emissions reporting to outside scrutiny.
Even the legal structure of the deal has American fingerprints. The European Union wanted countries' emissions targets to be legally binding, a no-go for Obama's negotiators who wanted to avoid having to bring the agreement to the Republican-controlled Senate for approval.
Instead, the Paris targets became "nationally determined," which allowed Obama to use his executive powers to adopt the deal on behalf of the United States, upsetting many Republicans who felt the deal should have gone to Congress.
But it also gave the flexibility for future administrations to revise their targets, which Obama's special climate envoy, Todd Stern, noted as he urged Trump to remain in the agreement. Rather than quitting Paris, Trump could "adjust" the Obama administration emissions target downward, Stern wrote last month in an opinion piece in The Washington Post.
"The agreement permits it, and I know because I helped negotiate that flexibility," he said.
Other countries insist they will remain committed to the Paris Agreement even without one of its key architects. But it remains to be seen whether they stick to their commitments on transparency and other issues that the U.S. had been pushing for.
Also, there are no guarantees that other countries won't decide to pull out as their governments or national circumstances change.
Japan, Canada and Russia eventually abandoned the Kyoto deal, rendering it meaningless.
AP