With the U.S. military intervention in Syria almost four years old and the Islamic State’s caliphate nearly eliminated, it’s past time to answer some basic questions about the war there: What are America's interests in Syria? What does the U.S. hope to achieve by remaining involved in Syria's civil war? What are the risks of sustained entanglement, and are they justified?

The United States intervened in Syria in 2014 to help regional powers reverse the gains the Islamic State had made. With their caliphate now a shrinking patch of desert, that aim is nearly achieved.

Many in the Washington foreign policy establishment say that the conflict cannot be resolved as long as Bashar al-Assad’s brutal regime remains in power. It’s true that his failure to address Syrians’ legitimate grievances sparked the civil war in 2011. But tragically, no credible alternative exists there today, let alone one who could govern Syria the way Americans would like. The likelier alternative is that no one rules, and the civil war continues killing Syrians, attracting foreign meddling and fanning extremism.

The Islamic State's collapse is bringing barely suppressed regional rivalries and enmities back to Syria's front lines. Every day, U.S. forces there risk conflict with Russia and other powers. The official rationale for our presence keeps changing without cohering into a clear argument about how a sustained U.S. military presence advances America’s interests. It is the responsibility of Congress, at a minimum, to demand answers.