The ironies are rich. Carbon emissions trading is an American idea…Now the Chinese are embracing it on a large scale.

When President Obama tried to tackle climate change in his first term, he pushed Congress to limit and put a price on carbon pollution, but the so-called cap-and-trade bill died in the Senate in 2010. Among the chief reasons: Lawmakers from both parties feared that any law to cut greenhouse gas emissions would harm the nation’s competitiveness compared with China, which was then emerging as the world’s largest polluter.

Since then, Republican lawmakers and presidential candidates have repeatedly cited China’s lack of action on climate change as the chief reason that the United States should not take stronger action.

On Friday in the Rose Garden, the story of how Washington and Beijing will fight climate change took a stunning turn as President Xi Jinping of China stood with Mr. Obama and announced that China would put in place its own national cap-and-trade system in 2017. Environmentalists hailed the announcement as historic and said that China’s move should effectively end Republicans’ main objection to enacting a domestic climate change policy.

“The ironies are rich,” said David Sandalow, a fellow at Columbia University’s Center on Global Energy Policy and a former senior official in the Obama administration. “Carbon emissions trading is an American idea. Now it’s an American export. The Europeans have moved forward in implementing it. Now the Chinese are embracing it on a large scale.”

But news of China’s cap-and-trade policy did not seem to change the views of a number of Republican presidential candidates.