The only point Jack Balkin misses in his commentary on the "Patriot Act II" is that there doesn't seem to be anything in the proposed law to check the Attorney General's finding that any group is a terrorist organization, and then stripping all its members of citizenship. I could be wrong about this, but so far as I can see, if this became law, Bush could proscribe the entire Democratic Party.
So long as we're thinking along those somewhat paranoid lines: Suppose you are one of the leaders of a party which forms a government even though it received only a minority of the vote at the last election, after being out of office for most of a decade. Suppose, furthermore, that the party has a quite radical ideological agenda which most of the country consistently rejects (so much so that an important and explicit part of your propaganda is to lie about your own positions). Exactly what incentive do you have to not create a police state?