President Barack Obama started strong by announcing the end of torture and the closing of Guantánamo, but he has recently taken a more equivocal attitude toward the Bush constitutional legacy. While rejecting his predecessor's extreme claims, he continues to assert the presidential power to hold terrorists without trial and to keep state secrets from the courts. And he has already issued his first signing statement denouncing a few provisions of the stimulus package as unconstitutionally limiting his executive prerogatives.

These decisions have unleashed a flood of anxious commentary about Obama's ultimate intentions. But the discussion has only served to divert public attention from the real question confronting the new administration. Barack Obama is no George W. Bush -- he will indeed cut back substantially on unilateral assertions of power. The big question is whether he will take effective steps to prevent the next president from reversing course yet again and using the precedents of the Bush years as a springboard for even more extreme assertions of executive authority.

Anything Obama does through executive order can be reversed by the next president through a countervailing executive order. The president's real challenge is to design a thoughtful process through which he could lead Congress to pass landmark legislation that would decisively repudiate the unilateralism of the Bush years.

The first step is to create a presidential commission on presidential power. Like great commissions of the past, it should include leading members of Congress and engage in a year-long process of deliberation. It should propose a series of landmark statutes that reinvigorate the founding principles of checks and balances. This would prepare the way for a serious collaborative effort between the president and Congress to enact realistic limitations into law before the next presidential election.

We have been here before. During the 1970s, Congress responded to the abuses of the Nixon years by passing the War Powers Resolution and the Emergency Powers Act. But these statutes were gravely weakened by the intense struggle for power between congressional Democrats and Presidents Richard Nixon and Gerald Ford. This time around, the same party is in charge of all the branches -- providing a precious opportunity to move beyond partisanship and confront the serious problem left to us by history.

We should not look upon presidential lawlessness as if it were an odd aberration of the Bush years. The abuses of the war on terrorism represents the third wave of illegality in a generation, coming after Watergate and the Iran-Contra fiasco. It is not enough for President Obama to resist the temptations of power. He should take the lead in a collective effort to diagnose the causes of and potential cures for the systematic tendency of the modern presidency to abuse its powers.

I am not calling for a truth commission that is primarily concerned with establishing the sordid facts about past abuses of power. The commission should be resolutely forward-looking, mining the past only to understand why existing statutes failed to effectively restrain presidential power. The challenge is to learn from experience and design better systems of checks and balances for the future.

This can only be accomplished by creating a special commission in which members of Congress and the administration don't try to score political points but work together to come up with serious proposals. This exercise might fail, of course, but it might also catalyze a serious collective effort to control the presidency's recurrent tendencies to break free of the rule of law. And if it did succeed, the resulting landmark legislation would serve as one of Obama's great legacies to future generations