The president exhibits not a hint of doubt, as though the events of the past two years had never happened. And yet, even though the word was never spoken, Iraq hung over the speech like a storm cloud. The burdensome military occupation of that country, and the continuing diplomatic fallout from the decision to invade, affects everything that the Bush administration will try to accomplish over the next four years.

The events in Iraq have proved that U.S. power, enormous though it may be, is incapable of forcing freedom to take root in even one country. It is certainly incapable of doing so in every country where tyrants rule. The president's rhetoric cannot conceal this fact.

But herein lies another danger. An unwillingness or inability to make good on the president's implicit promises could stir resentment abroad. From North Africa to South Asia, people living under the heel of autocratic regimes look to the United States for answers.

When the president says "it is the policy of the United States to seek and support the growth of democratic movements and institutions in every nation and culture, with the ultimate goal of ending tyranny in our world" people expect that the United States will take all necessary measures, including the use of military force, to eliminate the regimes that keep them in bondage.

When the United States follows through in some instances, as in Iraq or Afghanistan, but makes common cause with dictators in other places, in Pakistan or Saudi Arabia, the soaring rhetoric proves worse than silence, because it contributes to the perception that the United States is populated by hypocrites.

The president's speech suggests that the United States is committed to paying any price, including waging war against any and all tyrants, even if those regimes do not directly threaten us. But the United States does not possess an infinite reservoir of power. The collective American desire to spread the blessings of liberty abroad is rarely matched by a willingness to pay the costs necessary to make this happen.

If Americans can be convinced, as they were, briefly, in late 2002 and early 2003, that a tyrant poses a threat both to his own people and the United States, then altruism combined with prudence can mobilize the political will necessary to launch a war. In most instances, however, the costs are higher, and the benefits less obvious.

Here is where leadership comes in. The essence of leadership is to inspire, to stir others to action. The greatest leaders can convince their followers that anything is possible, that the benefits outweigh the costs. When they are wrong, when they exaggerate their own capabilities, or underestimate those of the enemy, the result is disaster.

If the country charges into the next four years with unrealistic expectations about what we can and cannot do--if the president adheres to the letter and spirit of his inaugural speech--then his actions will bankrupt the nation, dimming the light that has been an inspiration for those who yearn for freedom.

Christopher Preble is a founding member of the Coalition for a Realistic Foreign Policy. He is director of foreign policy studies at the Cato Institute, and he chaired the task force that produced Exiting Iraq: Why the U.S. Must End the Military Occupation and Renew the War against Al Qaeda.