PRESIDENT TRUMP is getting closer to exiting the Paris climate agreement. According to reports emanating from the White House, the president’s top lawyer shifted the internal debate last week. More meetings are to come. Yet the choice ought to be an easy one: Staying in the Paris accord is cost-free, but pulling out is not.

Paris exiters argue that the United States cannot remain in and revise downward the international commitment President Barack Obama made to cut U.S. emissions by 26 to 28 percent by 2025 — a pledge that, no matter how important for the planet, Mr. Trump does not want to keep. The White House counsel’s office reportedly lent its voice to this argument in a meeting last Thursday.

This is nonsense. World negotiators considered making the agreement’s climate commitment language stronger, preventing countries from backtracking on their pledges. They purposely declined to do so. The envoys who hammered out the agreement insist that they wanted to keep nations’ options open, in part because countries would otherwise lowball their international emissions commitments in fear of never being able to reduce their stated goals.

Arguments claiming otherwise reflect a grave — or purposeful — misunderstanding of the nature of the Paris agreement. At its core, it is a political pact among sovereign nations based on nonbinding “nationally determined contributions.” It does not and was never meant to formally bind countries to specific emissions commitments; instead it is intended to encourage voluntary cooperation and government-to-government pressure.

Moreover, the parties, not least the United States, get to decide what its terms mean. If the Trump administration is worried that a line in the agreement could be interpreted as improperly binding the U.S. government, U.S. officials can shape how countries understand the agreement’s language.

Or the president could simply ignore it. Nothing in the Paris agreement could stop him from keeping the United States in the system and Mr. Obama’s pledge on the books, and then simply declining to meet the pledge. It is fanciful to imagine that U.S. courts would interpret Paris, an agreement with almost no legal requirements, otherwise. Even this path would be better than pulling out entirely. Staying in keeps the Trump administration at the international table as potentially significant decisions are made on technology and decarbonization. Even some major coal interests have asked the president to remain in so that his administration can advocate coal-friendly carbon capture and sequestration technology.

Meanwhile, the president must not underestimate the cost of pulling out. Only two countries — Syria and Nicaragua — have declined to join the Paris agreement . Climate diplomacy has become a cornerstone of international engagement. By leaving Paris, the United States would surrender a huge amount of diplomatic capital and reputation — much more than it is already set to lose by unwisely reversing Obama-era emissions-cutting policies. Mr. Trump would hear about it for the rest of his presidency. And for good reason.