President Trump must order a second military strike against Bashar Assad’s regime.

That is, if the president intends to reinforce his red line against Assad’s use of chemical weapons.

Concerns have escalated due to increasing reports that Assad is employing chlorine and sarin chemical weapons against civilians in Idlib province. Idlib is the last major redoubt for rebel groups and thus a key target for the Syrian dictator. Over the weekend, health workers in Idlib reported victims of chlorine exposure following a helicopter attack. And last Friday, Secretary of Defense Jim Mattis echoed previous similar statements, warning that the U.S. might replicate its April 2017 military strikes, if it found evidence of new sarin attacks.

While the U.S. is working with international partners to account for any new chemical attacks, Russia is working hard to throw up as many obstacles as it can.

This cannot stand.

While nerve agents like sarin are far more toxic to the human body than chlorine (which normally causes great discomfort but fewer deaths aside from children or the infirm), on the battlefield, both are chemical weapons. Assad uses these weapons to terrorize civilians who might otherwise be able to take shelter from conventional bombings. By dangling the potential of imminent suffocation astride the sound of approaching aircraft, Assad inflicts grievous psychological damage on the civilian population. The dictator's broader intent to foster a sense of insecurity is also reflected by his attacks on hospitals.

Still, the U.S. has good reasons to deter Assad from future attacks.

First off, new strikes would show Russia and Iran that the U.S. remains committed to holding their ally, Assad, to account for his breach of President Trump's red line. If they sense any sign of American weakness, they’ll be emboldened to take more aggressive action against the U.S. in negotiations over Syria’s political future and in pursuit of their regional ambitions.

How do we know this? Because it's exactly what happened when Obama decided to abandon his own red line.

Fortunately, the U.S. also has good options with which to confront Assad.

For one, the U.S. military could engage forward deployed Syrian command units that have been linked to previous chemical attacks. Doing so would draw a specific line of contact between those forces carrying out chemical attacks and U.S. reprisals. It would also have a functional effect of degrading Assad’s ability to carry out new attacks. If Trump wanted to do more, he might even order a limited strike on regime command and control headquarters in Damascus.

That said, any new U.S. military action wouldn't be unduly risking war. While the Russians recently expanded their air defense network in Syria, the U.S. Air Force could strike Assad by launching ground to air missiles from a distance and without engaging Russian air defenses. More importantly, Assad, Iran and the Russians all recognize that U.S. strikes against Assad’s chemical weapons program would be with a specific focus, not undertaken in order to destabilize Assad's regime.

Regardless, for reasons of non-proliferation and basic morality, the time for action has come. That these attacks are still occurring nearly five years after President Obama first abandoned his red line, illustrates the continued suffocation of U.S. credibility in the lungs of Syrian children.

Update: Since publication, the language in the final paragraph has been clarified for greater clarity.