President Donald Trump just announced the United States will pull out of the Paris climate agreements, though it will try to negotiate for a new climate deal. Withdrawing from the agreement — a landmark deal that commits almost every country in the world to reducing greenhouse gas emissions to fight global warming — was one of Trump’s signature campaign promises. In recent months, however, it seemed less clear whether he would go through with it.

“We’re getting out, but we’re starting to negotiate and we will see if we can make a deal that’s fair,” Trump said from a press conference in the White House Rose Garden. “If we can, that’s great. If we can’t, that’s fine.” After the conference, France, Germany, and Italy issued a joint statement saying that the agreement can’t be negotiated, according to the Associated Press.

Reached at the end of 2015, the Paris deal was one of the most comprehensive climate change agreements ever passed; it is notable because it included countries like China, which pollute heavily but have not signed on to climate deals before. Under the agreement, former President Barack Obama had pledged to reduce US emissions by 26–28 percent of 2005 levels by 2025. But since his inauguration, Trump has initiated the roll back of several regulations, like the Clean Power Plan, meant to achieve those goals.

Advisers had been telling the president that he would benefit from staying with the agreement, according to The Washington Post. Foreign leaders lobbied him during his trip abroad. Apple CEO Tim Cook urged him to reconsider, while Tesla and SpaceX CEO Elon Musk tweeted that he’d spoken to Trump weeks ago about the agreement and was “cautiously optimistic.” (Upon hearing that Trump had decided to withdraw from the agreements, Musk tweeted that he was quitting the president’s advisory councils.) Trump’s daughter Ivanka Trump and son-in-law Jared Kushner, as well Secretary of State Rex Tillerson, a former chief executive of ExxonMobil, all suggested that he keep the United States in the deal.

Still, a group of 22 Republican senators recently sent a letter to the president urging him to keep his promise. And signs weren’t looking good at the end of the foreign trip, when he refused to publicly support the agreement. (The six other nations then reemphasized their own commitment in a joint statement.)

By pulling out, the US will join two other nations in the UN climate group — Nicaragua and Syria — that don’t take part in the agreement. (Nicaragua didn’t sign the agreement because its leaders thought it’s not strict enough; Syria has been embroiled in a civil war for six years.) China, the world’s top polluter, has vowed to go ahead with the deal regardless of the US’s inclusion, but there’s little doubt that the US pulling out will have big consequences. The United States is the world’s second largest greenhouse gas polluter and also the world’s largest economy. By dropping the deal, it could encourage other countries to leave as well, or perhaps simply not regard the guidelines.

In a statement, Obama said that he believes the United States should “be at the front of the pack” of nations working on curbing climate change. Still, he said he remains confident that despite the withdrawal of the US, “states, cities, and businesses will step up.”

Reactions from business leaders were largely negative. Amazon stated that it continues to support the Paris agreement. HP also affirmed its support for the agreement, adding that “the science [of climate change] is clear, the impacts are serious and the need to act is essential.” Similarly, Brad Smith, the president of Microsoft, tweeted that he was disappointed with Trump’s decision.

Even if fully implemented, the Paris agreement was never going to be a magical solution. The plan would still only reduce emissions by half as much as necessary to prevent a global temperature increase of 3.6 degrees Fahrenheit, scientists say. (It is considered crucial to avoid the 3.6 degree temperature increase in order to protect the planet.) But without the cooperation of the US, it now looks weaker than ever.