Few moments in our modern political history have been as eagerly anticipated as today's inauguration. After eight increasingly dispiriting years, the Bush administration at last exits the stage, to be succeeded by Barack Obama and the impressive Cabinet he has assembled. This page supported Obama's candidacy in both the Democratic primary and the general election; it was the first time since 1972 that we endorsed for president, and the first time in this newspaper's history that we supported a Democrat. Obama's victory was therefore welcome news to us, as it was for many millions of Americans.

Today is an occasion for celebration, for basking in the warm fulfillment of a long-deferred promise, as a black man stands before us as our president. In Obama, America has chosen a leader of eloquence and vision, of patience, intelligence and extraordinary capacity.

It is also, however, a moment in which we must pledge vigilance, not unqualified encouragement. Obama offers much promise, but he is confronted with problems of staggering magnitude. He will disappoint some supporters; already, there's grumbling to his left for having retained Secretary of Defense Robert M. Gates, for the elasticity in his timeline for ending the Iraq war, for his selection of evangelical pastor Rick Warren to deliver today's invocation, for his refusal to sanction same-sex marriage. Meanwhile, Obama has worried some of his more conservative supporters by tapping advocates of protectionism rather than free trade for key administration roles, an area in which Obama sent mixed signals during the campaign.

Governance demands more nuance than politics, and Obama's responsibilities as president, if honestly pursued, will sometimes fall short of his rhetoric as a candidate. We're braced for that, as the nation should be.

But recent history supplies a sobering lesson in what happens when support for a president dulls the skepticism needed to ensure public accountability. In the weeks and months after Sept. 11, 2001, the world rallied behind President Bush, and journalists were among those who sympathized too much. Claims of Iraqi involvement in the attacks and support for Al Qaeda were too readily accepted, as were reports that Iraq harbored weapons of mass destruction. The result was a war launched on false pretenses, with profound consequences for America's standing in the world and its identity at home. We once were a nation that would have been shocked to learn that the government spied on citizens without warrants, locked up suspects without trial, engaged in torture. But too many of us accepted those compromises of basic American principles as necessary accommodations for going to war.

Journalism was not to blame for those travesties, any more than it was for the administration's callous disregard for hurricane-swept New Orleans. But journalists' responsibilities during any administration of either party remain fixed: We must search out what the government would prefer to keep from the public; we must remind those in power of the pledges that brought them to office; we must encourage debate, not out of cynicism but in the conviction that openness and public discussion produce the most satisfying results in a democratic society.

The Constitution, which Obama today will swear to "preserve, protect and defend," includes only one profession under its guarantees of protection: a free press. It does so not to protect journalists, but in defense of the American people and their right to know their government. As President Obama sets forth in his historic administration, as Americans and people around the world invest their optimism and hope in his success, we pledge to watch him, to hold him to his work, and to report back.