Bush has admitted to the requisite "high crimes and misdemeanors" to allow for impeachment. It doesn't matter that these supposed crimes aren't truly crimes; he has effectively admitted to them being illegal and makes it impossible to claim otherwise. He has shown fundamental weakness leading up to the election that makes Congressional Republicans that much more vulnerable. Ultimately, the Democrats will gain control of the House, will successfully impeach the President, and he will likely be thrown out of office by a weak Senate Republican majority.
It is no secret that many Democrats (and certainly left-wing activists) want to impeach Bush. This drive started roughly on the day of inauguration in 2001. They've invented and refined charges throughout the past few years. Some of these have been completely debunked by the facts, others have hung around. For instance, the scandal of the Valerie Plame incident is that the prosecutor, after knowing who the leaker was the first day of the investigation, allowed the witch hunt to continue. The investigation also proved that not only did Bush not lie about Niger, but the claims were actually true.
However, the charge the Bush has violated the Geneva Conventions and tortured prisoners is one that cannot now be argued against by the President. By admitting that the terrorists have rights on the Geneva Conventions, he makes it impossible to turn around and say the decision not to grant them rights to begin with was legal. This is despite the fact that the Geneva Conventions are crystal clear that illegal combatants are entitled to no protections.
The Geneva Conventions protect only uniformed military who carry weapons openly. It does not protect spies, mercenaries, or terrorists. The fact that the language of the Geneva Conventions is clear on this point has not deterred the left from this rallying cry of human rights violations.
Discussions on what is or is not required in international law tend to border on the absurd. Usually the crowd that vigorously supports international law as binding is the same crowd that believes in the "living and breathing Constitution." In short, they believe that what is written and agreed upon doesn't matter; they believe that whatever is "progressive" is what the Constitution requires. The same is true of international law. Many scholars don't argue what is actually required in the treaties, they argue what they believe the law should be, and thus, it becomes much more invidious to defend against. Think of it as trying to hit a moving target.