OK, calmly, thoughtfully, reasonably. Credible evidence he "either knew about OR planned . . ." Well, which is it. Evidence is evidence. But, here's your real challenge. What would be the "formal accusation" to be deliberated and voted on by the House of Representatives? Not a court of law, the republican-controlled (for now) House. Admittedly, you'd only need a majority to impeach and send it to the Senate, but it's still a tall order.
Suppose you are able to somehow garner a majority vote (for something) in the House. Now, it goes to the Senate for a trial, with John Roberts presiding. You now need a two thirds majority to convict and remove from office. Come on. Put away the pipe dream. This entire discussion is a waste of space. The idea that Bush knew about or (what's really laughable) PLANNED (!!!) the attack is so preposterous only 1% of the entire American pollity (that lovable lunatic, liberal fringe) even considers it a remote possibility. People who have lived their entire lives under oppressive dictatorships and constant propaganda are rolling their eyes saying, "Come on!! "
The only people who believe this are that fringe group who want it to be true. If it weren't for this, they'd be clamoring for impeachment based on his mis-handling of the Iraq War (oh, wait, they are) or the War in Afghanistan, or his approval of the eavesdropping on American citizens communicating with al Qaeda operatives while we are at war. Let me get this straight, FDR was a great man and a great president, but Bush needs to be impeached.