In many ways, the fear of terrorism and the measures enacted to counteract a perceived threat can impinge freedom more effectively than the terrorist acts themselves. This must be resisted. America has faced greater challenges, such as the passing on of nuclear secrets, without compromising its commitment to due process.
The expansion of Executive power has placed in jeopardy the rights of Americans, foreigners entering America, and suspected terrorists captured outside US borders. The judiciary has tried to keep a check on presidential power, with Justice O'Conner emphasising "a state of war is not a blank check for the President".
The military commissions at Guantanamo Bay directly breach the Constitution. There is no convincing reason why a municipal court could not try all terrorist cases. A modified (civilian) criminal trial is permitted by the Constitution provided it is justified in light of a "time of war" or on grounds of "public danger". Classified information can still be legally protected.
The framers did not wish the judiciary to be the only check on unconstitutional legislation. For this reason, the power of veto was provided to the President, with the oath of office imposing an obligation to override unconstitutional legislation. But President Bush has only vetoed one bill and has signed others even while acknowledging concerns about their constitutionality.
A return to constitutionalism would check the present overreaching in two ways. First, it would restrict the President's ability to wage war without an official declaration from Congress, thus lessening foreign policy interventionism, which has historically been linked to an increase in terrorist attacks against American interests. Second, it would curtail efforts by the Executive to restrict freedom in the name of fighting the threat it has itself created through the pursuit of such an interventionist foreign policy.
Voters can take matters into their own hands. Assuming Congress will continue to support the President and disregard principle, the best check on power is to have Congress controlled by the party opposed to the President. Gridlock is perhaps the true friend of liberty.