He may be nutty, but how many aggressive actions has Iran actually performed in the last hundred years?
Much is made of Ahmadinejad and his supposed nuttiness and his Holocaust denial, but what has he actually done. Iran actually has a large Jewish population minority the largest of any Muslim country. Much is made of his supposed threat to Israel, but Iran hasn't invaded any country in the last century and more, whereas Israel has invaded all of its neighbors on several occasions and even annexed land in just the last 50 years, and the US has invaded two of Iran's neighbors. Iran is building nuclear reactors where Israel and the US already has them. Why can Pakistan, which actively supported the Taliban, and terrorists in India, and harbored bin Laden, allowed to legitimately own nukes (and is even a US ally) while Iran can't even have reactors?
As for supporting terrorism? All but one of the 9/11 hijackers were from either Saudi Arabia or Egypt, the US's supposed allies. There hasn't been a single instance of an Iranian suicide bomber anywhere. Iran however, was invaded jointly by the UK and Soviet Union in World War 2 to provide a seaport for shipping supplies to Russia. The US deposed its former democratically elected President in the 1950s. When the despotic Shah was deposed, and Iraq invaded Iran, the US actively supposed Iraq, and weapons of mass destruction (poison gas) were used against the Iranians, while the US at best turned a blind eye, and at worse, aided and abetted Iraq. During said war, the US shot down an Iranian civilian airliner and to this day refuses to apologize for the incident. And now, Iran is suffering from sabotage of its facilities and assassinations of some of its smartest scientists.
Or did you have the silly impression that bad relations were solely because of the current Iranian president, or that all the bad blood came solely from the Iranian side?