We kind of are. We have no leverage on Iran and everybody knows it. We can’t invade them, the American people won’t put up with another mid-east invasion. They’re already under embargo for various stuff. UN condemnation? Probably wouldn’t pass and really who cares. We really have no options.
Actually we do. Or did. The sanctions that were in place were wrecking their economy, most of which is owned by the mullahs personally. That's why Iran agreed to negotiate in the first place. But Obama lifted them as a reward for just sitting down with us, and threw away all leverage in the actual negotiations. Trump says he would walk out and double or triple the original sanctions until they begged us to negotiate.