I don't think that the current Iran nuclear deal is a good one. Bad people sucker punch the good guys all the time. A deal is only as good as the honor of the people making the deal.
That the attack on Pearl Harbor. While the Japanese were on their way to bomb it, the Japanese diplomats were stalling the US with talks of peace.
Hitler did the same thing with Europe and Russia.
Both N Korea and Iran have proven to be untrustworthy.
BTW, didn't we have a deal with Saddam Hussein?
So inferring that the Iran Deal is good, the real question is why would we consider doing a second bad deal?