George W Bush is literally destroying the fundamental structure of our government. We have, or at least we are supposed to have, a government with three seperate divisions: executive, legislative, and judicial. The executive branch is supposed to enforce the law, the legislative branch is supposed to make the law, and the judicial branch interprets the constitutionality of the law and settles disputes. Each power is supposed to be a check on the other. The executive has all the power to enforce the law, but cannot make it. If the president doesn't like a law, he may veto it. The legislature can make the law, but cannot enforce the law and cannot make law in violation of the Constitution. The Supreme Court cannot make its own law, and cannot enforce law, but has the last say on what laws are valid and how they ought to be applied and interpreted. Simple 4th grade politics, right?
GWB, however, does not play by the rules. When he does not like a certain bill, he doesn't veto it. He has never vetoed a single law to date. Instead, he signs the bill into law. He then issues a 'signing statement', a note announcing that he is not obliged to follow the law. He insists that, as president, no law has authority over the executive because of the clause in the constitution which reads "The executive Power shall be vested in a President of the United States of America." Of course, this clause was clearly not meant to mean the president is not subject to law (otherwise the constitution would not award veto powers to him because they would be meaningless.) In similar fasion, President Bush also ignores Supreme Court decisions and precedents whenever he pleases. He has already disobeyed over 750 laws since coming into office in 2001.
He believes that he can get away with this because he doesn't think the Republican-dominated Congress will stand up to him. He is right. Hopefully the Democrats will retake the House this November, in which case impeachment is a certainty. But the Democrats - even with a Senate takeover - will never garner enough votes in the Senate to actually remove him from office. So, even if he is impeached, he will still be free to do as he pleases. The level of partisanship in our country is so great that enough conservatives will continue to support him - because God forbid they don't get another anti-abortion vote on the Supreme Court.