Countries around the world—including Japan, Germany, the United Kingdom, China, and South Africa—condemned President Donald Trump’s decision to pull the United States out of the Paris Agreement on climate change on Thursday. Emanuel Macron, the president of France, even ended a speech decrying the withdrawal with the words “Make the Planet Great Again!”

But one reaction stood out. Justin Trudeau, the prime minister of Canada, tweeted:

The statement seemed to separate the United States, a large country of 320 million people, from the executive and legislative branch of its current national government. It’s a good public-relations move for the progressive boy-statesman who leads America’s northern neighbor—but there is also some truth to it.

Immediately after Trump’s announcement, the governors of New York, California, and Washington announced that they would work to uphold the U.S. commitment under the Paris Agreement. Taken together, those states encompass about 10 percent of the United States’ greenhouse-gas emissions, 20 percent of its total population, and 25 percent of its gross domestic product.

Other state and local officials also soon announced they would step up. Mark Dayton, the Democratic governor of Minnesota, said his state would pursue the Paris goals. And dozens of mayors across the country said they would continue to work to reduce greenhouse-gas emissions from their cities. Their number included Mitch Landrieu, a Democrat of New Orleans, and Jim Brainard, the longtime Republican mayor of Carmel, Indiana.

They may soon have a venue to do so. More than 30 mayors, 80 university presidents, and 100 businesses will soon submit their own emissions-reductions plan under the Paris Agreement, announced Michael Bloomberg, the former mayor of New York City, on Friday. They will call it “America’s Pledge.”

Bloomberg, currently the UN special envoy on cities and climate change, has also committed his philanthropical organization to donating $15 million in funding to the UN for climate-coordination efforts. Trump pledged to cancel an equal amount in his Thursday speech.

“Today, we want the world to know: The U.S. will meet our Paris commitment, and, through a partnership among American cities, states, and businesses, we will seek to remain part of the Paris Agreement process,” said Bloomberg in a statement. He said that the group will “aim to meet the U.S. commitment to reduce our emissions 26 percent below 2005 levels by 2025.”

“We are already halfway there—and we can accelerate our progress further, even without any support from Washington,” he added.

The politics of such a move are not hard to figure out. For mayors and governors with urban, college-educated, and especially younger constituents—in other words, for politicians whose voters do not resemble Trump’s—climate change is a winning issue. (Though some of the most climate-friendly actions they could take, like investing in public transit and supporting denser housing, may be less popular, as Josh Barro writes.)  

“Look, Donald Trump has absolutely chosen the wrong course. He’s wrong on the facts. California’s economy and America’s economy are boosted by following the Paris Agreement,” said Jerry Brown, the governor of California and a Democrat. He shared a press conference with Christiana Figueres, the former UN diplomat who led the negotiations that produced the Paris Agreement.

“The Californian economy increased 40 percent faster than the rest of the [U.S.] economy last year,” he added, despite “following policies that are even tougher than what Paris is calling for.” California has had some of the most stringent climate-change policies in the developed world since Arnold Schwarzenegger, a former Republican governor, called for them and signed them into law in 2006.

“Today’s announcement by the president leaves the full responsibility of climate action on states and cities throughout our nation,” said Jay Inslee, the Democratic governor of Washington, in a statement. “While the president’s actions are a shameful rebuke to the work needed to protect our planet for our children and grandchildren, states have been and will continue to step up.”

But can states and cities actually do something substantive on such a global issue? On that front, there are two avenues to watch.

The first is whether state initiatives can build business for renewable-energy companies in the United States. China and Germany, whose solar and wind sectors are most competitive with the U.S., aggressively subsidize their renewable-energy firms in ways that America does not.

China also builds renewable energy into the investment deals that it makes with developing countries: Accept China’s investment—and perhaps also its military presence—and it will build you solar panels and wind turbines. This creates the virtuous cycle of any investment learning curve: As companies build more solar panels, they get better at building them faster and cheaper. It remains to be seen whether U.S. states, taking a more piecemeal approach to climate investment, can let American firms keep up.

The second is whether these state and local programs can actually lower greenhouse-gas emissions. California’s climate programs already made up a significant part of the U.S. commitments under Paris, but ultimately it only emits about 6 percent of America’s overall share. (This is high among all states: Only Texas emits more, making up 13 percent of U.S. emissions.) But even if California, New York, and Washington were able to halve what they release into the atmosphere, the U.S. would not make its Obama-era Paris goal of reducing overall greenhouse-gas emissions by 25 percent.

This isn’t cause for climate-concerned Americans to give up hope—or for those states to abandon more stringent policies. Every molecule of carbon dioxide left out of the atmosphere makes the problem of climate change very slightly easier to address. And underlying trends, such as the continued decline in the cost of solar panels and wind turbines, will continue to chip away at American emissions. But it reveals what the logic of post-Paris state initiatives must be—a way to make a small dent in a big problem, a way to test policies before debuting them on a national scale, a way to suggest that Americans are not solely defined by their federal government.