Congress, which is supposed to push back against executive attempts to amass overweening power, has hardly played its proper role when it comes to George W. Bush. In the past, when evidence arose that the president had overstepped his authority, the Congressional response was generally to look for ways to make whatever Mr. Bush did retroactively legal. But the Supreme Court's decision on the Guantánamo Bay detention camp seems to have jolted even some of the most loyal Republicans back to reality. They are vowing that this time, they will not merely rubber-stamp presidential overreaching. Soon, Americans will get a sense of how seriously to take this newfound spine.

The court ruled, in a decision so strong that it sent shock waves through Washington, that Mr. Bush violated the Geneva Conventions and American law when he created commissions to try detainees outside established judicial procedure. The court rejected Mr. Bush's claim of a power to handle prisoners any way he wants and said it was up to Congress to set rules. 

This week, three Congressional committees will hold hearings on the issue. The White House predictably asked Congress simply to legalize Mr. Bush's policies. But a wide range of senators rejected that and called for a serious look at the basic question: whether and how existing rules should be changed to deal with terrorists who are not in any army.

The court said the military commissions, which Vice President Dick Cheney and his team cooked up without bothering to consult military lawyers, violated the Uniform Code of Military Justice, which has rules of evidence and process similar to civilian law. Congress could simply apply the military court to the Guantánamo prisoners. But the code was created to try members of the United States armed forces and some experts make convincing arguments its use would not be appropriate for terrorist suspects.