The bill that Congress will send to the President for his veto on Monday or Tuesday is unacceptable to President Bush because he believes that it allows Congress to meddle in warmaking by setting a timetable for withdrawal from Iraq.
Not quite. What it does do is allow Congress to do that which the Constitution demands — determine whether we are going to be at war or not. When last I looked at the Constitution, it was the President's job to determine how, but not whether, a war will be carried out, and it was the Congress's job to determine whether, but not how, a war will be carried out.
Had Congress come up with the idea of the "surge" and attempted to force that on the President, that would indeed be a usurpation of presidential powers. But to determine that, beyond a certain date, we shall not engage in hostilities in Iraq is certainly within the mandate of Congress. (It's been done before — think Somalia. But then we had a President who listened.)