This week, Maryland's congressional delegation will be called on to vote on a matter of the gravest national importance: President Barack Obama has asked lawmakers to authorize punishing military strikes against Syria in response to that government's use of chemical weapons last month to murder more than 1,400 of its own citizens, including 400 children. We urge our representatives in Washington to stand behind the president's resolve not to allow these heinous crimes to go unpunished. The use of military force is always a serious matter and never one to be undertaken lightly. But there are times when it becomes absolutely necessary because the alternatives are far worse. This is one of them.

After more than a decade of wars in Afghanistan and Iraq, Americans are understandably wary of becoming entangled in another protracted and potentially dangerous Mideast conflict. In Maryland, which voted overwhelmingly for Mr. Obama in last year's presidential election, public sentiment is just as lopsidedly against any U.S. military intervention in Syria. Members of the state's congressional delegation are keenly aware their constituents want no part of another overseas adventure that drains resources from projects at home and may end badly no matter what we do.

But Syria's use of chemical weapons against civilians represents the crossing of a line that the world cannot abide, and it must not go unanswered. The indiscriminate killing of innocent men, women and children with deadly poison gas is truly a "moral obscenity," in the words of U.S. Secretary of State John Kerry, that has rightly been condemned by international convention as beyond the pale of acceptable actions for any government, even during wartime.

To act now is not to say that the 1,400 Syrians killed by Mr. Assad's gas attacks matter more than the 100,000 killed by other means. They don't. What demands our intervention now is the dangerous precedent the unchecked use of these abhorrent weapons portends. Failing to enforce a decades old and nearly universal international norm against the use of chemical weapons would open the door to the wholesale slaughter of millions more people around the world by governments that felt no compunction against mass murder and genocide.

That's why Maryland's lawmakers in Washington must be very clear on what the upcoming vote in Congress is about — and what it is not. It is not about taking sides in Syria's ongoing civil and sectarian war. It is not about strengthening the "moderate" elements of the Syrian opposition or weakening "extremist" factions, which we have been unable to do so far, and it is not about repeating our mistakes in Iraq, where we invaded a country that posed no threat to us based on flawed intelligence about weapons of mass destruction that didn't exist. There is no question that Syria possesses chemical weapons and, as even skeptics of a U.S. intervention in Syria concede, no doubt that it used them against its own people.

What this week's vote is really about is whether the U.S. will stand by and do nothing while such atrocities occur. It's about whether a government that uses chemical weapons to flagrantly violate a bedrock principle of international law and decency will be allowed to commit unspeakably savage war crimes with impunity. And it's about whether the U.S. can summon the will to respond forcefully in upholding a world order that protects our citizens and those of our allies as well as the Syrian people from these awful weapons.

That responsibility that has been thrust upon us not because we are "the world's policeman" but because we are only country in the world that has the ability and moral clarity to punish Mr. Assad for his crimes against humanity. No lawmaker wants to buck the tide of popular sentiment, but faced with the monstrous evil the Assad government has, against all constraints of law and morality, set loose in the world, Maryland's representatives in Washington must take a principled stand alongside the president and support a limited but firm response aimed at convincing Mr. Assad and anyone else who may be contemplating using chemical weapons that they will pay a steep price for doing so.

This is a decisive moment for Maryland legislators and for a Congress that has not distinguished itself when it comes to getting the nation's most important business done. Authorizing military action in Syria is one of the most difficult decisions lawmakers will ever face, and we sincerely wish there were other credible options for them to choose from. But that's not the world we live in, which is full of risk and uncertainty. The only thing we can be sure of is that the consequences of doing nothing are likely to be even worse.