Robert Merry correctly observes that Trump’s planned “decertification” of the nuclear deal will announce to the world that the U.S. doesn’t keep its word. He asks:

But what are the consequences when a nation reneges on a solemn agreement with not just another nation but six other nations and a union of many more—with the entire world watching? How do other nations deal with a country that blithely casts aside the commitments it accepted through what were assumed to be good-faith negotiations?

The consequences for reneging on the deal will be uniformly negative for the U.S. Even if those consequences aren’t quite as bad as some experts are predicting, they will include damage to our government’s reputation, a loss of trust with close allies, and much greater skepticism if the U.S. asks for international cooperation on another difficult negotiation later on. The U.S. under a different administration may be able to repair the damage and regain the trust that Trump is about to squander, but it would be far better if one of Trump’s successors didn’t have to clean up his mess. Trump’s intention to blow up the deal is all the more alarming to other governments, especially our allies, because it is so clearly unnecessary and irrational.

The usual suspects that normally can’t shut up about the dangers to U.S. “credibility” are remarkably quiet these days. Most of the same people who absurdly worried that our entire alliance system would come crashing down if the government didn’t bomb Syria in 2013 have no problem with reneging on a carefully negotiated multilateral agreement. The people normally obsessed with “credibility” care about it only when it provides an excuse to launch attacks and start wars. Hawks tell us that American “credibility” is always and everywhere on the line if we don’t “do something” in response to this or that crisis, but when it comes to blowing up a major nonproliferation accord that has broad international support many of the same hawks are quite eager to do it.

Typical interventionist “credibility” arguments are nonsense, but there is a real political cost to breaking major agreements that our government negotiated. Reneging on the nuclear deal will further shake the confidence of allies in the quality of our political leadership, and it will make them less likely to support future U.S. diplomatic efforts than they would otherwise be. The U.S. may still be able to obtain their cooperation when it serves their interests, but the costs for the U.S. will be higher after Trump shows how unreliable our government can be. Trump won’t just be undermining the nuclear deal when he refuses to certify it in a few days’ time. He will also be making U.S. diplomacy less effective and more costly for future presidents.