I was going to cast about for various news articles from which I could assemble a response to Trump's predictable stupidity (really, who is surprised by this?). Sen. Flake, surprisingly, saved me the trouble:
Iran has already realized the benefits, which were front-loaded, in terms of sanctions relief and the release of these funds that were held in dispute, billions of dollars. And now, by our unilateral exit, it would give them license to renege on the nuclear aspects of the deal. So the West has upheld its end of the bargain, which was mostly front-loaded, and now Iran could get out of their agreement, and that just doesn’t make sense to me.
And also, I think, one of the most important things is, it’s just another signal to the world that we’re not a reliable partner. We begin negotiations, like on the [Trans-Pacific Partnership] and then we exit them. Or here, we actually execute an agreement, a new President comes in, and we’re out.
We’ve had a rules-based order that we have helped establish for 70 years post-World War II. And to see us just vacillate and move in and out, whether it’s tariffs that are imposed, and then certain countries exempted, it’s not so rules-based anymore, it’s ad-hoc, and we’re just not seen as a reliable partner.
We’re going to need to work with our allies, closely partner with them to address security challenges like North Korea, and the knock-on effects of us exiting here are not good.
There are also internal struggles in Iran between "moderates" and "hard-liners," and the U.S. walking away from this agreement strengthens the hand of the latter. Perhaps Netanyahu and Bolton imagine a war with Iran would be a good thing, and so they fervently desire it. Given how Israel left Lebanon (once a beautiful and peaceful country, now still a disaster area) and how the U.S. left Iran (no better off than we found it), one wonders what they are imagining for the future. I read somewhere the Congress could effectively override Trump's decision, but I don't hold my breath on that before the midterms, and afterwards I think is too late (by the agreements terms). I am convinced Trump just thinks he's "fixing" one more thing the "black guy" screwed up, and that's as much as he'll ever understand. Given his past statements against involvement in Iraq, and then hiring Bolton the neo-con's neo-con cheerleader, it is proof enough Trump can't hold one thought in his mind.
This will probably make things worse; it certainly won't make them any better.
ADDING: Trump talks on-line in Tweets (and does little better in person). Obama speaks on-line rarely, but in full, reasoned paragraphs. The best words, too.