Third and finally, arming the YPG amounts to a kind of defeat in the fight against the Assad regime. Some of the people in the U.S. government most against a closer relationship with the YPG are those who have spent the past five years working with the Syrian opposition groups. To the Syrian opposition groups, the YPG are collaborators. Indeed, in 2016, as the Assad regime and its supporters laid siege to East Aleppo, Syrian Kurds—albeit not the ones with whom the United States was working—more or less fought alongside the regime for periods. That led to alarmist stories like this one, which, while incorrect, were understandable if you weren’t following the details closely. As the head of the Pentagon’s Middle East policy shop at the time, I remember how difficult it was to get our aid and development workers to work with the Kurds in the city of Manbij after it was liberated from the Islamic State. The Syrians and Turks with whom our aid workers had been collaborating for the past five years were telling them that aiding the Kurds was tantamount to aiding Assad himself.

Nonetheless, toward the end of the Obama administration, we reached the conclusion—as subsequently reported by The Washington Post and others—that we would need to provide arms and training to the Syrian Kurds. And upon leaving the administration, senior administration officials have not been shy about laying out the logic of why they thought arming the Kurds would ultimately be necessary.

The debate over whether to arm the Kurds within the Obama administration was intense. It didn’t break down along the usual departmental fault lines, either: Within both State and Defense, officials responsible for safeguarding the relationship with Turkey—a NATO treaty ally—were often at odds with those whose primary responsibility was to defeat the Islamic State.

Both sides, I believe, argued their cases in good faith: Our able ambassador to Turkey among others repeatedly warned Washington about the effect arming the YPG would have on the U.S.-Turkey relationship, while our uniformed military commanders and others stressed they could not see a way forward to seizing Raqqa in 2017 without arming the YPG—absent the introduction of large numbers of U.S. troops in direct combat roles, something no one wanted.

Animating our sense of urgency was a desire to carry out assaults on Mosul and Raqqa simultaneously, something we were ultimately unable to do but which could have further stretched the Islamic State’s ability to defend itself. But what it really came down to—and what carried the day in the Obama administration and what seems to have finally carried the day in the Trump administration—is this: You’re simply not going to be able to seize Raqqa anytime soon without arming the Kurds with more powerful weapons than the ones they have now. In Iraq, we armed the Iraqis to the teeth before we sent them into Mosul. In Syria, we need to do something similar—albeit on a smaller scale—in order to go to Raqqa.