Josh Marshall says that “the argument about the need to maintain ‘credibility’ when deciding whether to withdraw from an ill-fated engagement is not one that, I think, can be dismissed out of hand,” before dismissing it in a non-out-of-hand kind of way. I think it sort of can be dismissed out of hand. Credibility isn’t an all-purpose commodity and, indeed, it’s not especially fungible. Whether or not the United States “has credibility” is rarely the issue, rather what matters is whether or not particular threats or promises we make are seen as credible.
This, in turn, is going to overwhelmingly be determined by our objective capacity to fulfill promises rather than by subjective assessments of our badassness. Under the circumstances, it’s very hard to see what kind of credibility benefit accrues to us from keeping the bulk of the US Army’s fighting strength in Iraq. Objectively, that only diminishes our capacity to do things in the world. What would really increase our credibility vis-a-vis, say, Iran would be for our threats to actually be credible the odds that we can somehow trick Teheran into believing we have the capacity to invade and conquer their country seem poor.