After a domestic drubbing at home, where disenchanted voters made clear they had heard enough of his clarion call for "hope and change," U.S. President Barack Obama scored a rare foreign-policy triumph in the sweeping deal with China to slash greenhouse gas emissions.
The pact may prove historic.
It signals the world's sole superpower regards China as a key partner in global leadership rather than just one among several great powers.
It provides the platform for Mr. Obama to carve out a key part of his legacy in combatting climate change – which he regards as the great challenge of the 21st century – and it, finally, makes good on the President's vague "pivot" to the Pacific.
After six years of scant foreign-policy successes – despite pocketing the Nobel Peace Prize – President Obama can still fashion a significant achievement if he can move the international community on combatting climate change. Getting China on board is a crucial first step.
As the world's two greatest polluters, with the two largest economies, the pact casts Mr. Obama and Chinese President Xi Jinping as equals and partners in a global leadership effort to forge ambitious international goals on cutting greenhouse gas emissions.
"It matters that the world's most consequential relationship has just produced something of great consequence in the fight against climate change," U.S. Secretary of State John Kerry said.
The key words are "the world's most consequential relationship."
By signing this bilateral pact with China, Mr. Obama may have reshaped the climate-change debate, both at home and internationally.
Engaging China as an equal plays to Beijing's yearning to be treated as a superpower by Washington. Mr. Obama acknowledged as much.
"If the United States is going to continue to lead the world in addressing global challenges, then we have to have the second-largest economy and the most populous nation on Earth as our partner," he said.
"A strong, co-operative relationship with China is at the heart of our pivot to Asia."
After years of vague talk about the Pacific pivot with little more than shifting some U.S. Marines to Australia and continuing uncertainty as to just how tough a military stand the United States might take if China asserted its controversial claims to disputed maritime boundaries, the two presidents may have shifted the rivalry to an emissions-cutting race.
Some critics claim the pact is largely symbolic but the symbolism of two great powers engaged in a joint effort with global consequences is powerful.
"This is a serious diplomatic breakthrough after years of unsuccessful efforts to do something big and joint that goes beyond clean-energy co-operation and gets to one of the most sensitive parts of climate policy," said Michael Levi, a senior fellow for energy and the environment at the Council on Foreign Relations.
The first test of the new joint Sino-American leadership may come next month when more than 190 nations will gather in Lima , Peru, to begin work on a new international climate-change agreement.
Gone will be the excuse that China has failed to curb its emissions.
"We are encouraging other countries to put forward their own ambitious emissions reduction targets soon and to overcome traditional divisions so we can conclude a strong global climate agreement in 2015," Mr. Kerry said in an op-ed piece timed to coincide with the Sino-American pact.
Climate-change activists hope the pact will give Mr. Obama additional leverage with nations such as Canada that have some of the world's highest per capita emissions.
"The U.S. is sending a message to those countries, and to the pro-fossil fuel governments, in Canada and Australia, that we are serious about putting climate at the centre of our international relationships," Ben Adler wrote Wednesday on the environmental news site Grist.
The deal is certain to reverberate domestically too as Mr. Obama charts the last two years of his presidency with both Houses of Congress firmly in Republican control after last week's midterm elections.
The bilateral pact with China was quickly denounced by Kentucky Senator Mitch McConnell, who will become Senate majority leader in January. It "requires the Chinese to do nothing at all for 16 years, while these carbon emission regulations are creating havoc in my state and other states across the country," Mr. McConnell said.
Even staunch backers of the President's pledge to cut emissions voiced skepticism.
The China pact is "a sign that President Obama is taking his climate legacy seriously and is willing to stand up to big polluters. But the real proof will be in the pudding," said May Boeve, executive director of 350.org, a leading environmental group. "There's no way approving the Keystone XL pipeline and additional fossil-fuel development is compatible with this pathway."