Indeed, the United States would be better served if policymakers abandoned the pretense that the Pentagon possesses any gift whatsoever for "standing up" foreign military forces. Prudence might actually counsel that Washington assume instead, when it comes to organizing, training, equipping, and motivating foreign armies, that the United States is essentially clueless.
Exceptions may exist. For example, U.S. efforts have probably helped boost the fighting power of the Kurdish peshmerga. Yet such exceptions are rare enough to prove the rule. Keep in mind that before American trainers and equipment ever showed up, Iraq's Kurds already possessed the essential attributes of nationhood. Unlike Afghans and Iraqis, Kurds do not require tutoring in the imperative of collective self-defense.
What are the policy implications of giving up the illusion that the Pentagon knows how to build foreign armies? The largest is this: subletting war no longer figures as a plausible alternative to waging it directly. So where U.S. interests require that fighting be done, like it or not, we're going to have to do that fighting ourselves. By extension, in circumstances where U.S. forces are demonstrably incapable of winning or where Americans balk at any further expenditure of American blood -- today in the Greater Middle East both of these conditions apply -- then perhaps we shouldn't be there. To pretend otherwise is to throw good money after bad or, as a famous American general once put it, to wage (even if indirectly) "the wrong war, at the wrong place, at the wrong time, and with the wrong enemy." This we have been doing now for several decades across much of the Islamic world.
In American politics, we await the officeholder or candidate willing to state the obvious and confront its implications.