Too bad for the House... Bush does NOT need Congressional authority to attack Iran. The President has the authority to strike Iran (or any other target for that matter) for 30 days. He only has to notify Congress. After 30 days Congress either authorizes him to continue the war, or they ask him to stop. There is no basis of impeaching him. 30 days are enough for an aerial/naval war against nuclear/military facilities.
It doesn't take a BASIS for impeachment.
They can impeach him for anything or nothing. They can make it up. They can use vague terms about "abusing the power of office".
There is no legal standard for what constitutes a valid article of impeachment.
Impeachment is a political process not a legal one.
If a simply majority of the House says that he's committed an impeachable offense and votes to impeach him, he's impeached. There's no APPEAL from that.
Then he just has to win in the Senate.
The House can impeach him again if they like.
They could use impeachment as a no-confidence vote.
Bush didn't pardon the Thanksgiving turkey right? Misdemeanor! Impeach! It's sort of like filibustering judges. I have heard the hand-wringing that it's illegal or unconstitutional or whatever. Of course it isn't. It's political, and Congress sets its own rules, which are not reviewable by the judiciary.
So, just to be clear, an impeachable offense is whatever a simple majority of the House of Representatives SAYS is an impeachable offense. There's nothing more to it than that.