Everyone is making a big deal of this, but in reality, the Paris Accord was never ratified by Congress so it was not worth, to us, the paper it was written on.
Exactly. Trump messed up. He should have said "My hands are tied." He could have "apologized" by saying that the best legal scholars in the U.S. have bluntly informed him that, under American Constitutional Law, the U.S. cannot abide by the rules of the Accord--because Obama's commitment of the U.S. to the Accord was flagrantly illegal. Trump could have sheepishly declared that Obama was deceiving the American people and, by extension, deceiving the whole world when he signed the treaty completely apart from the Constitutionally required approval from the United States Senate. In other words, Trump could say, "The American President is not the legal representative of the United States under such circumstances--even if a conniving President and his co-conspirators convince you that he surely does represent the United States."
Trump could go on to say that we now have the same problem with the Iran treaty. He could say "My lawyers have pointed out that it is my sworn Constitutional duty to declare the treaty with Iran void--because it is obviously a grotesquely illegal agreement--and I am taking the opportunity to do so right now. Furthermore, I have to inform the world that we are right now preparing to move against Iran if they try to retaliate against our Constitutional Republic for revoking what is obviously just a phony document, a flagrantly illegal treaty."
(I would love it if Trump could go on to say that "This very week, we have empaneled a federal grand jury which I believe will yield criminal indictments against Obama and his co-conspirators for treason against the United States of America.")