If we accept that premise, which I'm not necessarily willing to do, then Bush can be impeached for all manner of action which congress might deem "inappropriate."
I was merely pointing out that successful impeachment efforts almost always have a legitimate "crime" as the basis for the action.
One of best reference sources regarding impeachable offenses is The Law of Presidential Impeachment. Also instructive is the memorandum written by Hillary Clinton regarding the possible impeachment of Richard Nixon. You might also try
A Century of Lawmaking for a New Nation: U.S. Congressional Documents and Debates, 1774-1873 httpp://memory.loc.gov/ammem/amlaw/
....which contains the debates among the framers regarding the Constitution, including the provisions on impeachment.
Many believe the idea that impeachment has something to do with justice or punishing someone for crimes. The purpose if impeachment it to remove a "bad" official from office so he can't do any more "bad" things before the next election. That's it. It's not about affecting his legacy. It's not about "doing right."
Bush will be out of office in seven months. He is under close scrutiny. It is unlikely that he is going to do anything in the next seven months to bring the country down.