AP Photo

In the coming weeks, President Barack Obama will make the most difficult choice a commander in chief can face: whether to send more troops into harm's way.

The challenge of making the right decision was dramatized recently by the grim disclosure that Gen. Stanley McChrystal, the top U.S. and NATO commander in Afghanistan, has warned that unless he gets more troops the eight-year war there "will likely result in failure."

The general provided a bleak catalogue of misaligned military operations, a corrupt Afghan government, and an increasingly lethal insurgency. He wants more troops and civilians to execute a nation-building counterinsurgency strategy that he hopes will reverse the slide. He says success is still achievable. As the commander on the ground, Gen. McChrystal...