I've been thinking about this legislation and why Bush would sign it even though he knows its unconstitutional.
Presidents, even some of our favorites, routinely sign legislation they know (or suspect) to be unconstitutional.
The best example of this: The federal budget itself. By some estimates, roughly 2/3rds is unconstitutional.
The charge that Bush is knowingly violating his oath would carry more weight if it were followed up with calls for his impeachment. I don't, as of yet, hear any such calls.
So I don't take such charges seriously.