Here’s an interesting news item: The Administration is reportedly preparing to bring military and political leaders of the Syrian rebels to Washington so that they can lobby Congress to approve U.S. military intervention against Assad. I mention this because it seems to highlight a significant evidentiary problem that Congress has to deal with in deciding momentous questions of foreign policy. To inform their decision, members of the House and Senate will have intelligence reports that the President has chosen to share, testimony from executive branch officials, press reports, and whatever information can be gleaned from the rebel leaders. But virtually all of these sources are heavily biased in favor of intervention. Having already decided to pursue military action, the President and his subordinates are disinclined to highlight evidence that might weaken their case. The Syrian rebels are, for obvious reasons, unlikely to present anything other than an argument for intervention. And the U.S. media is both hawkish and sub-optimal as a source of military and foreign intelligence, given frequent lack of access to inside information. Analogizing to domestic litigation, the situation is like having one party to a lawsuit provide virtually all of the evidence, and forcing the court itself to find any support for the counterargument. If the adversarial system elicits truth, this approach may do the opposite. Moreover, the problem is particularly acute in foreign policy because Congress is unable to employ its usual tools of investigation outside the territory of the United States. Committees, for example, can’t subpoena foreign leaders to testify, staff members can’t gather eyewitness accounts by deposing non-citizens living abroad, and relevant governments may not volunteer relevant and reliable information. In many cases, members of Congress try to make up for the information gap by traveling overseas to meet with foreign leaders and observe conditions, but the instability in Syria renders even that option unavailable. Don’t be surprised if the overwhelmingly one-sided configuration of evidentiary inputs results in Congress approving the use of force.