Not a friend; the enemy of our enemy. Basic political lesson there.
Johnnie, you're right about the isolationists. There's always somebody else they SAY we ought to have fought first - Iran, N Korea, Syria - but as the Red Queen said to Alice, it's "jam every other day, but never jam today."
Fine, so now the main enemy of Iranian regime is removed and Iran is becoming the main regional power. Is it another "basic political lesson"?
About "enemy of our enemy", it was Iran who helped America to win in Afghanistan as it was Iran/Russia allied Northern Alliance which did the key part of the fighting against Taleban. Is the removal of Saddam Hussein a secret reward to Iran?