Since responding to an allegedly government-led chemical weapons attack with a missile strike on a Syrian air base earlier this month, the administration of President Donald Trump has offered conflicting messages about its ultimate goal in Syria.

In the immediate aftermath, Secretary of State Rex Tillerson told ABC News that beyond enforcing a redline on chemical-weapons use, "There is no change to our military posture."

Nikki Haley, the U.S. ambassador to the United Nations, however, told CNN, "There's not any sort of option where a political solution is going to happen with (Syrian President Bashar) Assad at the head of the regime."

As for Trump, he's been all over the map. After Assad used chemical weapons in 2013, Trump tweeted, "President Obama, do not attack Syria. There is no upside and tremendous downside." After the latest attack, though, he said, "My attitude toward Syria and Assad has changed very much."

So, must Assad go?

Yes, but not simply because of the chemical weapons. After all, Syrian rebels may have used them as well. Rather, Assad must go because he is an impediment rather than an asset in the necessary defeat of the Islamic State. Assad can deliver neither security nor stability. The ongoing civil war in Syria began with protests that erupted because of Assad's mismanagement and spread because of his ham-fisted response.

Consider the case of Hamza Ali al-Khateeb: Security forces arrested the 13-year-old during a protest and, weeks later, returned his mutilated body to his parents. Rather than bury their son, they allowed Arabic satellite stations to film his corpse.

Further, Assad does not necessarily want to defeat the Islamic State.

Prior to U.S. air operations over Syria in August 2014, only Assad's air force had been operating over Syria. Yet these forces did not once bomb the Islamic State's de facto capital, the Syrian city of Raqqa. The reason? Assad wants to give Syrians a binary choice: Either support him or fall to Islamic State extremism.

As far as Assad is concerned, the greatest threat to his survival is any politician or group seen as competent and more moderate. Assad is not an outlier in his tolerance for the Islamic State. He may be secular, but he is no secularist.

So what is the solution? Isn't the devil we know better than the unknown? Years of fighting and abandonment have radicalized any remaining moderates who, at any rate, have shown themselves no more capable of stabilizing Syria than Assad. Fighting may be intense around Idlib and Homs, but parts of Syria are calm and rebuilding. Girls walk to school and municipalities provide water, electricity, and even pick up trash in Syrian Kurdistan.

Rather than engage in grand plans, world leaders should recognize Syria for what it has become: a collection of loosely-linked federal cantons and work to eliminate the terrorists in between.

As for Assad, even the Kremlin has stated that Russia's support is not unconditional. That provides an opportunity for a swap at the top. With Assad gone, any new face, even one from his inner circle, opens the door to new possibilities.

Michael Rubin is a leading Middle East expert, former Defense Department official, and resident scholar at the American Enterprise Institute, a think tank in Washington, D.C. He can be reached at AEI, 1789 Massachusetts Ave. NW, Washington, D.C., 20036.