This image released on April 7 by White House press secretary Sean Spicer on Twitter shows President Trump receiving a briefing on the Syria military strike from the national security team via video teleconference at Trump’s Mar-a -Lago estate in West Palm Beach, Fla. (White House/AFP)

Recently I wrote that since the war against the so-called Islamic State, or ISIS, keeps expanding, Congress needs to revisit the blank check for waging war that President Trump and former president Barack Obama have claimed it wrote. With the attacks on Syria on Thursday, the Trump administration made that need for congressional deliberation even more urgent.

U.S. intervention in the Syrian civil war might, or might not, be the right thing to do. Bombing the Assad regime is certainly viscerally satisfying. But without legislative authorization, it is hard to think it’s legal.

Let’s look at the law.

We can go back to Obama’s decision not to take similar action in Syria in 2013 to see why. Back then, the former head of George W. Bush’s Office of Legal Counsel, Jack Goldsmith, wrote that “an intervention in Syria would extend the president’’s war powers under the Constitution beyond where they have gone before.” That is, it would be based solely on an aggressive reading of the president’s Article II title as commander in chief, not on domestic or international law.

Let’s consider domestic law. In 2001, after the Sept. 11 terrorist attacks, Congress passed an Authorization for the Use of Military Force (AUMF) — which does not apply here. Conceivably, the 2001 AUMF can be extended to cover groups tenuously linked to Sept. 11, such as ISIS or al-Shabab. But the use of military force against a sovereign state — Syria — cannot fit under that blanket.

As for international law, the U.N. Charter allows the use of force against member states only in self-defense, or when the Security Council has authorized such force “to maintain or restore international peace or stability.” Neither condition holds here.

The Washington Post's Louisa Loveluck reports on the regional reaction to President Trump's cruise missile strike against a Syrian airfield in response to a chemical attack that killed dozens of civilians. (Louisa Loveluck, Jason Aldag/The Washington Post)

Yes, presidents have used force unilaterally in the past. But those instances were different.

In the past, presidents have acted unilaterally without seeking prior congressional authority. But those circumstances have had common characteristics not present in this week’s Syrian case — something Obama’s lawyers ran up against as they tried to craft a rationale in 2013.

The most common past rationale has been self-defense. That can be an easy case to make, as with President Jimmy Carter’s (failed) 1980 rescue attempt of American hostages in Iran, or President Bill Clinton’s 1998 missile strikes after al-Qaeda bombed U.S. embassies in Africa. We could include here President Ronald Reagan’s 1986 bombing of Libya (after an attack in Germany that killed a U.S. serviceman).

In other cases, presidents have been more imaginative in their interpretation of what counts as an attack upon the United States. For instance, President George H.W. Bush explained his 1989 invasion of Panama was a response to Gen. Manuel Antonio Noriega’s “reckless threats and attacks upon Americans in Panama [that] created an imminent danger to the 35,000 American citizens” there. Reagan justified his 1983 invasion of Grenada along similar lines, saying that it was “first, and of overriding importance, to protect innocent lives,” and not just any lives — “American lives are at stake.”

Second — in addition, or instead — presidents have relied on multilateral support or treaty demands, often in part because of humanitarian concerns. Even Reagan, in invading Grenada, was careful to stress that the Organization of Eastern Caribbean States had invited the United States to respond; that it was doing so in concert with other nations in the region (albeit nations whose battleship inventory was thin, or even nonexistent); and that “this collective action has been forced on us by events that have no precedent in the eastern Caribbean and no place in any civilized society.”

Similarly, in attacking Somalia (1992), Kosovo (1999) and Libya (2011), U.S. administrations were able to cite both humanitarian concerns and treaty obligations (e.g. with the United Nations, NATO, or both). All these attacks certainly frayed War Powers Resolution limits; for instance, the WPR specifically rules out inferring authority to use force from treaty obligations. Nonetheless, such circumstances gave the presidents cover, and Congress failed to overturn their actions.

Presidents have been wrongly trying to extend their war power authority.

Of course, even when Obama sought congressional approval to use force in Syria, he didn’t concede that he had to. (At the time, a certain Twitter user named Donald Trump heartily urged the then-president to seek such authorization.) Indeed, in a 2013 Rose Garden statement, Obama argued that “I believe I have the authority to carry out this military action without specific congressional authorization.”

Meanwhile, “senior administration officials” grumpily told The Washington Post that they debated “the implications of ceding executive authority over war powers to the legislative branch.”

But such a formulation — while hardly new to Obama — frames war authority as purely executive in the first place. It is not.

The Syrian civil war certainly presents a tragic humanitarian dimension and near-constant violations of international norms. But these are not new this week; nor, as yet, is there an international mandate for intervention there. If there is to be a domestic mandate, it must come from congressional deliberation.

Washington Post reporter Dan Lamothe explains why President Trump launched 59 Tomahawk missiles at a Syrian military airfield on April 6 and what this means for the fight against the Islamic State. (Sarah Parnass,Julio Negron/The Washington Post)