The role that the U.S. Congress has assumed for itself as a player in foreign policy exhibits an odd and indefensible pattern these days. Senator Chris Murphy calls it a "double standard," although that might be too mild a term. On one hand there are vigorous efforts to insert Congress into the negotiation of an agreement on Iran's nuclear program. The efforts extend even to attempts to interfere in the details of what is being negotiated, as reflected in a string of amendments being considered in debate in the Senate this week on a bill laying out a procedure for Congress to pass a quick judgment on the agreement. On the other hand there is inaction, with little or no prospect of any action, on an authorization for the use of military force against the so-called Islamic State.

That combination is exactly the opposite of the roles Congress should play, taking into account first principles of when and why the people's representatives ought to weigh in on the conduct of the nation's foreign relations. Going to war is probably the most consequential thing the nation can do overseas. It entails substantial costs to the nation, and as recent experience should remind us, carries the risk of far greater costs, both human and material, than may have been anticipated at the outset. It is quite appropriate for such a departure not to be left solely in the hands of the executive.

The impending nuclear agreement with Iran entails none of those things. No Americans are being put in danger. There is no risk of being dragged into wider or longer commitments to pacify, occupy, or do something else to land overseas. There is no drain on American taxpayers; in fact, to the extent that completion of the agreement will lead to lessening of economic sanctions on Iran, it will entail lifting of what has also been an economic burden on the United States. As the subject of a complicated international negotiation that involves several other states and in which compromises on all sides are essential, for national legislatures to intervene in the details with specific requirements or demands is simply a recipe for failure of the negotiations. It is entirely appropriate for this agreement, like the great majority of international agreements that the United States makes, to be a matter of executive action until fulfillment of the terms of the agreement requires legislative action.

Several reasons account for the inappropriate reverse nature of where Congress is weighing in and where it isn't. Debate about the nuclear deal and about the bill bearing Senator Corker's name isn't really about Congressional prerogatives, especially given that the bill is not necessary for Congress to express itself however it wants about the substance of whatever agreement emerges from the negotiations. It instead has been about whether opponents of any agreement with Iran would be able to use a procedural mechanism for increasing their chances of killing the deal. This is reflected in the current grumbling by diehard opponents of an agreement who see that the current version of the Corker bill does not give them as much of a chance for doing that as they had hoped.

The inaction on an authorization for the use of military force has a couple of explanations. The more respectable one is the inherent difficulty of crafting suitable language when the intended purpose of the military action is not as simple and straightforward as, say, defeating another nation-state. Instead the purpose involves a terrorist phenomenon in which both the geographic and temporal extent of what needs to be done is uncertain. It is hard to come up with a legally precise formula that gives the executive the authority it needs to do something effective but also imposes meaningful limits, in terms of time and place, on the military operations. The draft resolution that the administration sent to Capitol Hill has some questionable language; fixes to it will be necessary but difficult. The difficulty is not a reason not to try.

Not trying gets to the second explanation for the inaction, which is political pusillanimity. Members of Congress realize that taking a stand on such things involves taking a risk, Some members feel burned either for opposing one Persian Gulf war that turned out to be a smashing victory, or for authorizing another Persian Gulf war that turned out to be a costly mess. It's easier for them just not to commit themselves and to stay quiet while the White House asserts executive authority and uses military force anyway. And that posture is a cop-out.