Hearing a presidential candidate "nuance" his position on the war in Iraq seems to surprise some in the media. But it shouldn't.

Events on the ground - not politics in Washington - are what will likely drive any administration's decisions. One reason is the reality of international affairs. America can't just impose its wishes on the world. The rest of the world gets a vote in how things turn out.

Presidents must respond to the global situation they face, even if that means flouting political promises they made in Iowa a year before.

One thing's certain: The anti-war movement in the United States won't drive foreign policy. Indeed, such factions never do.

Anti-war movements are a fixture of American culture dating back to the Revolution. Americans argue about their wars before, during and after. That's an inherent feature of how democracies go to war. Nevertheless, the role of dissenters in shaping American attitudes is particularly overblown. Americans like to make up their own minds.

Anti-war movements don't drive public will. They ride the crest of the public opinion wave. For example, there was a vocal and well-organized movement to keep America out of World War II. It was led by aviator Charles Lindberg, an all-American hero, and Gerald Nye, the irrepressible populist senator from North Dakota. Their following collapsed after Pearl Harbor.

Today's anti-war movement didn't so much shape public opinion as feed off it. Americans had been frustrated by the lack of progress in stabilizing Iraq after the conflict and the death spiral of violence dragging the country into civil war. But contrary to what anti-war activists fervently claimed, that angst wasn't the result of Americans' feeling repelled by a long war or by causalities.

Americans are averse to failure, sending their sons and daughters and national treasure into harm's way when there seems no purpose. Americans can accept sacrifice as long as they believe that the cause serves their national interest and that the goal is attainable.

A new U.S. strategy in Iraq has stemmed violence, put Al Qaeda on its heels, frustrated Iran's hope to dominate the country and renewed hopes for establishing a stable state. Indeed, for many Americans, the ferocity with which Al Qaeda and Iran have tried to exploit conditions in Iraq is a grim reminder of how dangerous America's enemies really are.

In turn, Americans have become more sanguine about meeting our responsibilities in Iraq, even though it appears the effort will take years and all the troops won't be coming home soon. The anti-war movement is continuing the charge, but most Americans aren't following.

Nor do the anti-war movements share any political coherence. All they have in common is opposition to the war. When that cause goes away, the movement will fall apart. This is already happening with the anti-Iraq war movement.

It's ironic to watch the veterans against the wars in Iraq and Afghanistan trying to mimic the Vietnam era "Winter Soldier" project by allegedly documenting widespread atrocities by U.S. military forces.

The Vietnam project produced sensational, but highly dubious, results. America's Army was never the "barbarian horde" that young John Kerry famously claimed it was. Likewise, virtually every one of today's men and women in uniform serve honorably, as well. Most Americans believe in their soldiers, so a new "Winter Soldier" project will only further distance the movement from mainstream politics.

The Constitution designed a government that insulates the president from such political factions. A newly elected president has a mandate from the American people and usually is able to rise above the demands of divisive groups.

Only one American president, Gerald Ford, was ever forced to quit a war. He is the exception that proves the rule. Congress voted to cut funds supporting South Vietnam even though by 1975 our country had largely put the war behind it. The problem was Ford was an unelected president with no support from either the left or the right.

In contrast, the next president will have more than enough political will to push back against a now wilting anti-war movement. The winner will, however, have to put America's interests first and have the courage to deal with the realities of international affairs rather than the whims of political factions here at home - no matter what he has promised.

James Jay Carafano is a senior research fellow for national security at The Heritage Foundation.