Opponents of the 2015 Iran nuclear deal often complain that the deal doesn’t address the nefarious ways in which Iran is expanding its influence and further destabilizing the Middle East. Such concerns, while valid, are no reason to blow up the agreement, as President Trump is recklessly trying to do by pressing his administration to declare, with absolutely no evidence, that Iran is in violation of the terms.

Critics often ignore the fact that the deal was intended to keep Iran from producing a nuclear weapon, a crucial and necessary goal. They also ignore the fact that the deal is working, as the International Atomic Energy Agency, which rigorously monitors Iran’s activities, and even Mr. Trump’s own State Department have certified.

One can imagine the challenges the United States could be facing if the deal did not exist and this administration were grappling with two nuclear-armed adversaries at once. But it is not; North Korea, which traded fiery threats with Mr. Trump in recent days, has 20 or more nuclear weapons. Iran has none and, thanks to the deal, is significantly constrained in its nuclear ambitions for years to come.

Instead of questioning the deal, Washington could turn its attention to concerns about Iran’s nonnuclear activities. Sunni Arab monarchies fear that Shiite-majority Iran will establish a “Shiite crescent” from Afghanistan to the Mediterranean. Iran is undoubtedly throwing its weight around, but it would help to remember that this is partly a result of America’s 2003 invasion of Iraq and ouster of Saddam Hussein, once a formidable check on Tehran’s adventurism.