[azernik]

The Paris Agreement included an explicit clause allowing parties to exit it after giving notice of withdrawal. It did not go out of effect immediately on Trump's election, but the administration went through the legal procedure.

The NPT has much stricter terms for withdrawal, which in any case Iran has not followed.

(The better and much more relevant analogy would be the JCPOA. That's what happens when the US does foreign policy by "executive agreement" instead of treaty. Foreign countries should not value them more than the paper they're written on.)