Rhetorical bows notwithstanding, Mr. Obama’s recent nonbinding, no-detail, anti-carbon accord with China is less about Chinese emissions than it is about America’s climate politics. Read here from the WSJ, how Obama has found the perfect climate-change partner: “A technocratic elite that can instruct the bourgeoisie how they must light their homes and commute to work.”

All of which suggests that this accord is less about China than American climate politics. One of the main arguments against U.S. carbon rationing has been that such economic masochism is pointless as long as Chinese and Indian emissions continue to grow. Mr. Obama will now claim the Middle Kingdom is signed onto his anticarbon agenda, even if its promises are distant and vague.

In return for Mr. Xi’s assurances, Mr. Obama pledged that the U.S. will cut emissions by as much as 28% below 2005 levels by 2025. This implies doubling the annual pace of CO2 reductions over the 17% marker that Mr. Obama set in 2009. So using the Sino-American deal as cover, Mr. Obama will now say he is obliged to impose a new burst of aggressive carbon regulations, no matter the harm to U.S. growth.

The difference is that American governance, unlike China’s, is supposed to follow the rule of law; companies can’t refuse to obey regulations because the CEO’s brother-in-law belongs to the Party. Yet most of the rule-makings to enforce Mr. Obama’s promises to China will emerge from his administrative-state tunnels like the Environmental Protection Agency without a vote in Congress. Under this President, the political systems of the East and West may share more features than patriots care to admit.

This condominium between the world’s No. 1 and No. 2 carbonizers is also supposed to inspire a new global climate treaty in Paris next year, but other nations may draw a different lesson about Mr. Obama’s negotiation methods. The Chinese no doubt saw how much the President wanted an agreement and that he would accept nearly anything that could pass as one.

Meaningless global warming promises are much easier than corralling weapons of mass destruction in North Korea, or convincing Beijing to fight Islamic State, or for that matter stopping Chinese cyber-attacks on U.S. military and corporate targets. Mr. Xi must have been delighted to see a U.S. President agree to make America less economically competitive in return for rhetorical bows to doing something someday about climate change.