The White House has warned the Syrian regime of Bashar Assad to avoid using chemical weapons again. The United States has evidence, it says, of Syrian regime preparations for a chemical attack.

And the U.S. was clear: If Assad does launch another attack, he and his military will "pay a heavy price."

The Trump administration is right to take this stance.

First off, the Syrian regime was always likely to carry out another chemical attack.

As I noted following the last atrocity in April, Assad would have regarded President Trump's military response that time as a test. He wants to see whether Trump has the endurance to resist axis escalation. By "axis," I mean the coalition aligned with Assad in Syria. It consists of Iran, various Shia militia groups and Russia.

Regardless, that axis has been angered by Trump's surprising resistance to its aggression. This was evidenced last week, when Russia threatened to target U.S. fighter aircraft in response to the American downing of a Syrian jet.

By carrying out another chemical attack, the axis believes it can compel Trump to abandon his anti-Assad efforts on the ground in Syria. It hopes the U.S. will accept its contention that the only way the conflict will be won is if the U.S. accepts Assad. Russia's hand lurks closely in these preparations for another attack. Putin would love to understand whether Trump has any interest in standing up for U.S. interests when the stakes get tough.

Second, this is a proportional and forward-leaning response.

After all, no attack has yet taken place. By warning Assad that he should not take action, the U.S. gives him a way out. In the perfect scenario, Assad will get back in his box and no lives will be lost.

Yet by issuing this threat so publicly, rather than via diplomatic back channels, the U.S. is also putting its credibility on the line. That lends weight to this threat to take action against the Syrian military if an attack does go ahead. And it strengthens Trump's word as a leader. Credibility on the international stage is important.

Third, the U.S. has a vested strategic interest in preventing Assad's continued use of chemical weapons.

Alongside the deterrent principle in discouraging other global actors from using weapons of mass destruction, there are specific concerns related to Assad's situation. Most notably, as I debated with Fox News' Tucker Carlson, the U.S. has a very significant interest in assuring Syria's Sunni population (and Sunni populations across the Middle East more generally) that it will not allow their sectarian annihilation.

Again, Assad's war against his own people has had a very specific target: Sunnis. And if the U.S. is seen to yield to this brutality, groups like the Islamic State will benefit. That's because those groups will be able to say, as they said in Iraq after 2011, "If you're a Sunni, your only hope of security is to pledge allegiance to us."

Ultimately, the risk of war here is overstated. As I've explained, no nation in the region, nor Russia, has any interest in going to war with the U.S. And while Assad is a brutal killer, this isn't about morality per se.

Instead, it's about preventing the new understanding that chemical weapons can be used with impunity. And ensuring that the U.S. plays a leading role in checking the sectarian impulses that flow from atrocities such as the use of chemical weapons.