Let's not forget the whole "Iraq has WMDs" excuse Bush had - which was quickly debunked, and added to the weakened credibility of the US Administration. The only way the US could whole-heartedly support an invasion of Iran is, yes, a massive, ill-advised terrorist attack on the USA that is traced back to Iran. Which Iran isn't going to be dumb enough to give.First the op requires a full scale invasion and we learned the lesson by 2007 that going light footprint and restrictive with the ROEs at the start didn’t work out too well.
This was at a time quite a few democrats on the Hill had put all their political coins behind opposing Bush’s foreign policy in the Middle East as in Harry Reid the Senate Majority leader declaring the war in Iraq lost.
Going from that to Congress authorizing a war, a draft or at least a massive professional conventional forces build up would require a terrorist attack on the US at least somewhat traceable to Iran linked Shia groups that rivals 911.
Remember the whole mess with Filipino Monkey?