As President Obama nears a decision on Afghanistan, he faces a partisan divide in public opinion that is pulling him in opposite directions. His recent statements about the decision suggest that he is trying to accommodate the views with a war strategy that can be successful and contained.

This is the dilemma Obama faced when, as a candidate, he cast his lot with Afghanistan while opposing the war in Iraq. The issue that was avoidable then, but is no longer, is how to put down al-Qaeda and the Taliban without being drawn into an endless conflict in a nation that has swallowed up outside forces through the centuries.

The lengthy policy debate inside the administration has spun out of control as it nears its finish, with damaging leaks and counterleaks. White House...