Afghan children play near a lake on the outskirts of...

Afghan children play near a lake on the outskirts of Herat. (Dec. 13, 2012) Credit: Getty Images

Wars can't be fought and won according to a timetable. If calendars could control, then all wars would be over by Christmas.

American soldiers should never be put in harm's way unless it's vital to our national interests. And if it's a vital interest, they should stay until the mission is accomplished.

To suggest that they can be withdrawn from a mission by an arbitrary date - regardless of progress made or lost - implies that the mission is not important, that they shouldn't have been sent in the first place.

Our armed forces don't fight for the sake of fighting. And they don't want to fight on a clock. They fight to serve our nation. And they would rather stay longer and do the job right than come home too soon.

The military ethos revolves around the commitment to serve, to sacrifice their own safety and the comfort of family, rather than leave an important job undone.

"But don't you want the troops home by Christmas?" By focusing on the date - rather than the consequences of the proposed action - the question evades the major point. It's like asking someone if they'd like to have a thousand bucks - without telling them you were going to get the cash by robbing their grandmother.

Consequences matter. Yes, the world is a big place. But that doesn't mean that, when faced with a thorny problem, you can just walk away and relocate to less stressful climes.

This is the 21st century. The world is a much small place than it was 50 years ago, and it's getting smaller by the day. The Vietnam War should be viewed as a cautionary tale about embracing a just-walk-away strategy.

In 1975, a Congress sick of conflict simply cut off aid to South Vietnam, and watched from the sidelines as the country collapsed under an armed invasion. But the U.S. suffered serious consequences price for turning its back on its interest in Southeast Asia.

Emboldened by what it saw as an America in retreat, Moscow ramped up both its nuclear arms program and its support for insurgencies worldwide. Within five years the planet was a much more dangerous place.

That slide stopped only when President Reagan reversed the course of American foreign policy. The more he exercised "peace through strength," the less the U.S. actually had to do prove its mettle on the field of battle.

The U.S. position today seems as precarious now as in that post-Vietnam era. Once again we have a White House conducting nation security operations according to a timeline rather than the reality of conditions on the ground.

In Iraq, the U.S. pulled back too quickly. As a result, the Associated Press is now reporting al-Qaida has twice as many operatives there now as it had just last year. In Afghanistan, the president gave commanders half the troops and time they requested to get the job done before he began his arbitrary drawdown.

Not surprisingly, the U.S. is in trouble in Afghanistan as well. Foreign fighters are flooding into the country to learn from the Taliban how to fight and kill Americans.

Pulling back as our interests becoming increasingly insecure is ill-advised. Yet the White House is compounding the problem by trying to cash a massive "peace dividend" even as its strategies are making the world less peaceful. That means that, as problems grow and fester in the coming months and years, the United States will have less capability to respond to them.

Rather than pick a date, the U.S. would do better to ensure that its interests are protected before it walks away. And it should commit, as well, to maintaining the forces and capabilities needed to secure its interests in the foreseeable future.

James Jay Carafano is vice president for foreign and defense policy studies at The Heritage Foundation.