dKos takes a break from obnoxious candidate-shilling and sockpuppetry to let Kagro X explain to us just how willing the president is to undermine separation of powers and even the Rule of Law, and not just in order to keep his own fat out of the fryer, but even merely as a guy who doesn't believe he can (or should) be stopped.
Riffing off of what Kagro X is arguing here, I think this is what makes it so difficult for Congress to battle the president effectively on matters of potential criminal misdeeds in the Executive. The president doesn't give an inch, he doesn't compromise, he doesn't believe in comity or bipartisanship, or oversight, for that matter. Every single move they make will be fought to the last man, every request will be denied, every demand will be stonewalled, because George W. Bush doesn't believe in governing: he believes in winning. The federal government, to him, is not a governing body that hammers out compromises in order to work together according to the will of the people; rather, it is a battleground where the Forces of Good battle the Forces of Liberal to the death, where one side must Win and the other Lose, where willingness to compromise is a sign of weakness and the desires of the masses are not something to legislate, but something to be reshaped in the Battle of Messaging that takes place right after the legislative Victory.
It's like trying to run a congress with Beowulf as president.
Furthermore, he has been convinced by the neocon cabal in the White House that, once he sends troops into another country, he is virtually omnipotent until the conflict is over. And enough Republican senators have bought into his bullshit that they will filibuster every bill he doesn't like, and vote however he wants them to on every bill, and use every legislative maneuver in the book to defeat bills he doesn't like.
How do you fight such a monster? One of 2 ways: 1. you capitulate to it, appease it until it leaves, trying to eek out as many little wins as you can get without really angering the behemoth so that it destroys as little as possible in that time-- and pray to God that another monster doesn't take its place-- or 2. you set your jaw, steel your gaze, and resolve to fight it to the death, even if that means jeopardizing the entire system, because you cannot allow it to go undefeated, you cannot allow the theory of the Unitary Executive to go irrefuted, you cannot let future presidents think that this sort of behavior is permitted.
The problem is that, in Congress, where you have to have at least a majority to do anything and nearly half the body is already working for the president, if you can't get your whole caucus to commit to the latter strategy, you're forced to accept the former.