Can the US military preserve decades of wartime experience?

The order had already come down. The assault on a fortified Mahdi Army position in the Iraqi city of Karbala was off.

It was August 2004. Army Col. Peter Mansoor and his brigade had spent days preparing to clear the enemy stronghold, located across from one of Shia Islam’s holiest sites. Then coalition officials canceled the operation, deciding the political risks were too high.

The enemy…