Because Syrian President Bashar al-Assad continues to possess weapons of mass destruction, and has now used them twice, a U.S. response was warranted.

On Tuesday, Syrian President Bashar al-Assad’s regime launched a chemical weapon attack against his own people—many of whom were sleeping. More than 70 men, women, and children were killed by the nerve agent Sarin, which typically causes agonizing asphyxiation and death.

According to CNN, Assad denied he had used the nerve agent on his own people, insisting, instead, that a routine bombing mission hit a rebel-operated nerve gas “factory.” Assad employed a similar excuse after a 2013 Sarin gas attack, arguing anyone could make Sarin, which he called the “kitchen gas.”

Chemical weapons experts find this explanation highly improbable. Sarin, especially the binary agent type used in the attack, is extremely difficult to manufacture outside of a controlled lab environment.

While the world universally condemned Assad for this attack, it was clear that Russia would not quickly or easily allow a United Nations action aimed at curbing Assad’s power. Because Assad’s attack employed a weapon of mass destruction that even the Nazis refused to use, Tuesday’s actions represented something much more sinister than even the indiscriminate slaughter of small children.

Because Assad continues to possess WMDs, and has now used them twice, a U.S. response was warranted. President Trump acted decisively on Thursday night, sending 59 cruise missiles to destroy a large military installation and airfield Assad had used to launch his nerve gas attack. While some cheered this act, others—especially on the far Right—decried it as unnecessary, illegal, and further evidence that the U.S. meddles where it should not. I disagree, and think Trump got it exactly right with his response.

Assad’s Attack Is a Threat to U.S Interests

Assad, like other madmen and dictators around the world, has been murdering his citizens for years. Approximately 500,000 civilians have been killed in Syria’s multi-year civil war, and we have largely left Syria and its people to figure out the conflict on their own. I do not applaud the doctrine suggesting the United States should be the world’s policeman, nor do I believe it is the United States’ place to punish the perpetrator of every atrocity. The world is a big place, and U.S. resources cannot create universal peace and harmony.

But, much more than a heinous war crime, Assad’s actions represent a dangerous precedent that is directly threatening to U.S. interests at home and abroad. His use of WMDs in time of conflict represents a rare use of a weapon that more than 175 nations have banned, and has only been used in war four other times since World War I (once by Assad in 2013).

If Assad were allowed to act with impunity—which is essentially what happened following his 2013 use of Sarin—every dictator the world over would rightly understand that the United States turns a blind eye to the development and use of WMDs of all kinds, even in the back yards of U.S. allies. How can the United States assert the moral right to call for the denuclearization of North Korea when we care little about the use of a different WMD in Syria? What do we do when a WMD isn’t merely used in our allies’ back yard, but in our own?

Trump Is Telling Syria Not to Mess With Protective Norms

That’s why Trump’s actions were so important. Far from committing us as a participant in Syria’s civil war, or putting us on a collision course with Russia, Thursday’s precision strike sent a robust message.

It was the strongest indication in years that the United States does care about the development, possession, and use of WMDs. It demonstrated that the United States has the ability to assert its power to protect allies and force change at any time, in any location around the world.

It showed that when the United States makes a demand, unfriendly regimes should take note and comply. It re-drew the red line that use of a WMD so strongly represents. Finally, it reinforced in the mind of Assad and every other rogue dictator the world over that those 59 cruise missiles could just as easily have been sent to visit the presidential palace in Damascus, or in some other capital city.

The United States is not the world’s policeman. But the United States is the leader of the free world. In that role, the United States demands certain minimum standards of international comportment. The use of WMDs has been universally decried, and represents a direct threat to our interests in the Middle East and worldwide. Trump was right to assert those interests, and burnish our reputation as the shining city on the hill we’ve been for so long.