Several lawmakers on Capitol Hill are questioning the president's legal authority to launch a retaliatory strike on Syria for their use of poison gas on civilians.

The president's authority to use force in any situation without direct congressional authorization has been an issue since the Vietnam War.  Congress passed the War Powers Act in 1973, and it is drawn extremely broadly, giving the president vast authority to carry out military operations overseas for 90 days without seeking congressional approval.  But the conditions under which the president can act are fairly specific.  He can act only in response to an attack or if there is an imminent threat. 

The expected Syria operation being planned meets neither of those criteria.  But Syria represents an example of the extreme limitations of the War Powers Act. 

NPR:

Sen. Tim Kaine, D-Va., who has become a leading voice advocating for Congress' responsibility to approve military action, said the president should release the memo before any strikes.

"Without congressional authorization, any military action President Trump takes in Syria that isn't in self-defense is illegal," Kaine said in a statement on Wednesday.

Continued Kaine: "And while he's at it, he should also release the secret legal memo that reportedly justifies the airstrikes on Syria last year – which clearly haven't deterred Assad – and that the president is apparently now using as precedent for unilateral military action."

Kaine told NPR this week that while in general he would support airstrikes against Assad, he does not believe that the president can unilaterally bomb a sovereign country like Syria without congressional authorization.

Another Trump critic, Connecticut's Democratic Sen. Chris Murphy, told NPR that although he condemns the Assad regime's reported chemical attacks, there are obvious limits on Trump's authorities to act.

"We're a nation of laws, and we have a Constitution that says very clearly that it's Congress who gets to decide who the United States can fight wars against," Murphy said.

"The president can take military action without congressional permission if the U.S. is attacked or is at risk of imminent attack – but that's not what happened here," he said.  "If the president thinks he a found a loophole that lets him attack other countries without authorization, he needs to show that justification and make that case to the people."

Debate over the privileges and responsibilities of ordering military action have dogged presidents since Vietnam. In 2011, for example, Republicans complained that Congress hadn't been adequately consulted about the military operations then-President Barack Obama ordered against Libya.

Later, when confronting the crisis Syria, Obama found himself painted into a corner after having declared the use of chemical weapons would cross a "red line."  When Assad used them, Obama decided that he had the authority to order an attack against the Syrian regime, but also decided, out of principle, to ask Congress to authorize it.

Lawmakers did not; the measure went nowhere.  The United States joined a coalition of nations in attempting to remove Syria's chemical weapons, which ultimately did not stop chemical attacks there.

If anything, Libya was less of a threat than Syria to the U.S., but the "responsibility to protect" civilians from Gaddafi's brutality supposedly overrode other considerations. 

Of course, Assad makes Gaddafi look like a Sunday school teacher when it comes to slaughtering civilians.  And yet a far more important issue is upholding the ban on chemical weapons to prevent their use from being accepted.  I feel certain that somewhere in the legal reasoning being considered by the White House is defending the Chemical Weapons Convention, which forbids the manufacture and use of poison gas.  It may be a stretch legally under the law, but the flaws in the War Powers Act have made it virtually useless anyway. 

No one has actually gone to court to challenge the constitutionality of the act, and for good reason; both the Executive and Legislative Branches of government are afraid of the outcome.  And so a delicate balance is maintained where Congress can threaten and the president is somewhat constrained by the act.

A president should not have the authority to go to war without the consent of Congress.  But an action like bombing the Syrian air force to prevent the further use of chemical weapons was never imagined by the Founders and has been justified in the past as falling under the president's authority as commander in chief.  There will be some grumbling by some lawmakers if we attack Syria, but most members of Congress are resigned to the president's power to send our military in harm's way for just about any reason he sees fit.