WASHINGTON -- I come to this moment of national decision with deep concerns about the next president. His victory is likely to unleash an ideological and vengeful Democratic Congress. In the testing of a long campaign, Barack Obama has seemed thoughtful, but sometimes hesitant and unsure of his bearings. He promises outreach and healing, but holds to a liberalism that sees no need for innovation. And as the result of a financial panic that unfairly undermined all Republicans, Obama has stumbled into the most dangerous kind of victory. A mandate for change but not for ideas. A mandate without clear meaning.

But a presidential election is more than a political choice; it is a moral dividing line. It involves not just the triumph of a majority but a transfer of legitimacy that binds the minority as well. This is a largely undiscussed topic in modern political debate: legitimacy. It is a kind of democratic magic that turns votes into authority. It does not require political agreement. It does imply a patriotic respect for the processes of government and a determination to honor the president for the sake of the office he holds.

In the last few decades, the magic of legitimacy has seemed to fade. Opponents of President Bill Clinton turned their disagreements (and Clinton's own human failures) into an assault on his power. Some turned to insane conspiracy theories, including accusations of politically motivated murder. After President George W. Bush's re-election, elements of the left began their own attack on his legitimacy, talking of impeachment while repeating their own lunatic theories of deception and criminality.

After a deserved honeymoon, the new president is likely to find that the intensity of this bitterness has only gathered. Because of the ideological polarization of cable TV news, talk radio and the Internet, Americans can now get their information from entirely partisan sources. They can live, if they choose, in an ideological world of their own creation, viewing anyone outside that world as an idiot or criminal, and finding plenty who will cheer their intemperance. Liberals have perfected this machinery of disdain over the last few years. Given the provocation, the same approach is likely to be turned against the new president by the right as well.

Barack Obama's first years may well be dominated by a recession and a swiftly arming Iran. Some conservatives will be tempted to take joy from his inevitable struggles; others to spin conspiracy theories from his background and associations. It will be easy to blame every emerging challenge on the faults and failures of an inexperienced young president. But it will be more difficult for me.

I remember the vivid days of possibility that follow a presidential victory. I happened to be in the Roosevelt Room in January 2001 just as the portrait of Teddy Roosevelt, heroic on horseback, was moved over the fireplace, where it hangs during Republican administrations. And I know someone will be watching when Franklin Roosevelt is moved back to the place of honor, feeling the same hope and burden that I felt.

There is a tremendous sense of history and responsibility that comes with serving in the White House. You gain an appreciation for the conflicted choices others have faced -- and for the untamed role of history in frustrating the best of plans. It becomes easier to understand a president's challenges, and harder to question his motives. Ultimately, I believe that every president, and the staff he hires, feels the duty to serve a single national interest. And ultimately we need our presidents to succeed, not to fail for our own satisfaction or vindication.

This presidency in particular should be a source of pride even for those who do not share its priorities. An African-American will take the oath of office blocks from where slaves were once housed in pens and sold for profit. He will sleep in a house built in part by slave labor, near the room where Lincoln signed the Emancipation Proclamation with firm hand. He will host dinners where Teddy Roosevelt in 1901 entertained the first African-American as a guest; command a military that was not officially integrated until 1948. Every event, every act, will complete a cycle of history. It will be the most dramatic possible demonstration that the promise of America -- so long deferred -- is not a lie.

I suspect I will have many substantive criticisms of the new administration, beginning soon enough. Today I have only one message for Barack Obama, who will be our president, my president: Hail to the Chief.