Iran has been our biggest failing in the region since the 1980s. Afghanistan? Arm some Mujaheddin, abandon them fostering resentment and inadvertently leading to the creation of both the Taliban and Al-Qaeda, then go to war with them a couple decades later when they come back and attack us in the worst act of terrorism this country has ever seen. Iraq? Give weapons to a ruthless dictator, watch him gas his own people, back track on your support only after he invades a country friendly to American business interests, get in two different wars, execute the leader and leave the region completely destabilized, inadvertently creating a breeding ground for ISIS. But Iran will be different! For one thing, it's larger than Iraq and Afghanistan combined... so if you thought the fallout was bad from our dealings with those two, just you wait!
A wise person once said that those who fail to learn from history are doomed to repeat it. Apparently every single Republican since the 1980s has decided that was written by a communist, and our only real chance for success is to bomb some other Middle Eastern country, in a strategy that has been failing to produce positive results since the days of Saladin.