Secret Service members observe the congressional picnic in Washington on Friday. (Chris Kleponis/Bloomberg News)

It’s not quite clear why President Trump canceled pending airstrikes against Iran meant to retaliate against Iran’s destruction of a U.S. surveillance drone. It probably wasn’t because he had a sudden desire to ask Congress to weigh in on the matter. House Speaker Nancy Pelosi (D-Calif.) said she was not even notified of the decision to attack. But any sustained military action against Iran will, indeed, require congressional authorization.

There are two statutes — and two articles of the Constitution — to consider here. Article I, of course, grants Congress the power (and duty) to declare war. Article II makes the president commander in chief of the armed forces. What that offered in independent authority was not obvious. Elbridge Gerry (of “gerrymander” fame) said at the constitutional convention that he “never expected to hear in a republic a motion to empower the Executive alone to declare war” — though the framers certainly contemplated the president’s ability to “repel sudden attacks.” After World War II, though, presidents took advantage of being commander in chief of huge standing armies to, well, command them.

As the Vietnam War wound down, though, legislators passed the War Powers Resolution to ensure they were involved in decisions concerning “the introduction of United States Armed Forces into hostilities, or into situations where imminent involvement in hostilities is clearly indicated by the circumstances.”

In the War Powers Resolution, presidents are given authority to use force when there is (1) a declaration of war; (2) a specific statutory authorization; or (3) “a national emergency created by attack upon the United States, its territories or possessions, or its armed forces.” Option one is self-explanatory; option two is less so than it might seem, as we’ll discuss further below.

But let’s look at option three. Does a downed drone count as American “armed forces”? Or does it count as a “national emergency”? We’ve seen that the Trump administration has a very low bar for what constitutes one of those. As I have written before (about Syria, or the Islamic State, or Syria again), presidential uses of force without War Powers Resolution authorization have often invoked self-defense. That includes President Jimmy Carter’s (failed) rescue attempt of the American hostages in Iran in 1980 and President Bill Clinton’s 1998 missile strikes that retaliated for al-Qaeda’s African embassy bombings. In other cases, presidents were more imaginative in their interpretation of “attack upon the United States.” For instance, President George H.W. Bush explained his 1989 invasion of Panama as a response to Manuel Antonio Noriega’s “reckless threats and attacks upon Americans in Panama [that] created an imminent danger to the 35,000 American citizens” there. The 1983 invasion of Grenada was publicly justified by President Ronald Reagan along similar lines.

Such an argument might plausibly cover a direct retaliatory strike against Iran but would not seem to extend to a more sustained conflict. Indeed, the Pentagon reportedly warned the airstrikes might lead to “spiraling escalation” endangering U.S. troops in the region — in short, to “imminent involvement in hostilities.”

This brings us back to option two — that of statutory authorization. The administration would have to request it — unless it can argue that Congress already approved a wider war with Iran. Apparently this occurred — wait for it — 18 years ago. Various reports suggest the Trump administration is considering citing the 2001 Authorization for the Use of Military Force as the legal grounding for extended military action.

That measure was passed shortly after 9/11 and thus applies most obviously to al-Qaeda and the Taliban regime in Afghanistan. Over time, it has been stretched far beyond those initial targets to include the Islamic State and various terrorist groups operating on the African continent. Let’s say those extended the Authorization for the Use of Military Force to targets that were six degrees of separation from al-Qaeda. But claiming the authorization extends to approval for war with Iran would stretch it further — perhaps six to the sixth degree. Iran, after all, is a sovereign nation whose government was not involved in the 9/11 attacks — and whose leaders, as New York Times reporter Charlie Savage points out, are Shiite Muslims whom the Sunni devotees of al-Qaeda consider to be apostates.

Some members of Congress have sought to amend and update the Authorization for the Use of Military Force, but those efforts have not been successful. A cynic might argue that legislators find the status quo politically useful, allowing them to complain about presidential action without taking responsibility.

The administration might adopt other arguments instead, grounded in the president’s implied authority as commander in chief. Brian Egan and Tess Bridgeman at Just Security usefully lay out the Justice Department’s Office of Legal Counsel (OLC) opinions holding that Article II gives the president the power to initiate the use of military force when there is an important “national interest” to do so (as defined by the president) and when the force does not constitute war. “Military operations will likely rise to the level of a war only when characterized by ‘prolonged and substantial military engagements, typically involving exposure of U.S. military personnel to significant risk over a substantial period,’” OLC argues. This allowed the Obama administration to claim, for example, that 2011 military operations in Libya did not count as “hostilities” for War Powers Resolution purposes; the Trump administration in turn claimed the same was true of its 2017 and 2018 airstrikes against Syria over its use of chemical weapons. War with Iran would, again, seem to be on a different plane.

That might not matter to those holding extreme views of presidential power — for instance, someone who would argue that even the 1991 Gulf War did not require congressional approval. (That someone would be William P. Barr, now in his second stint as attorney general.) But it should matter to Congress.

For instance, legislators should keep in mind that OLC opinions are not privileged over other legal analysis. And while quite frequently lawmakers’ opinions on presidential power fall along partisan lines — presidents of one’s own party seem to magically accrue additional constitutional authority — bipartisan Senate coalitions have formed recently that suggest a hardening backbone on foreign policy matters. For example, angered by the Trump administration’s generous reaction to Saudi Arabia’s killing of journalist Jamal Khashoggi, senators have voted to cut off support for Saudi air attacks on Yemen and to block arms sales in the region. Might the specter of another Middle East war be a prod to institutional — really, constitutional — pride?

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