To do so, Mr. Erdogan hopes to tar the pro-Kurdish People’s Democratic Party as a terrorist front and steal votes from the Nationalist Movement Party. He has used the current crisis as a smoke screen behind which to launch an air war against militants from the Kurdistan Workers’ Party, or P.K.K., in Iraq and artillery strikes on the Democratic Union Party, or P.Y.D., in Syria. He has also unleashed a new wave of repression aimed at Kurds in Turkey, which risks plunging the country into civil war.

Image A demonstration against the Kurdistan Workers' Party on August 16 in Istanbul. Credit... Ozan Kose/Agence France-Presse — Getty Images

This strategy might help Mr. Erdogan win an election, but it is severely undermining the fight against the Islamic State. By disrupting logistics and communications links between the P.K.K. in Iraq and the P.Y.D. in Syria, Turkey is weakening the most effective ground force fighting the Islamic State in Syria: the Kurds.

We would do well to remember that it was P.Y.D. forces, with logistical support and reinforcement from the P.K.K., that liberated the city of Kobani last year and recently retook Tal Abyad, cutting off a key route for infiltration of arms and foreign fighters for the Islamic State.

America’s agreement with Turkey might yield more effective airstrikes, but that will come at the cost of losing the valuable real-time intelligence provided by Kurdish forces that is so crucial for targeting purposes.

In the long run, undercutting the Kurds will be extremely damaging to the anti-Islamic State effort since allowing Turkey to create a no-go zone for Kurdish forces will not carve out territory for moderate fighters; instead, it risks creating a safe haven for Islamist groups like the Nusra Front and Ahrar al-Sham, whose growing strength will exacerbate the toxic sectarianism and ethnic violence that has plagued Syria for the past four years.

Secretary of Defense Ashton B. Carter’s recent declaration that “we do want Turkey to do more in the fight” against the Islamic State prompted a pledge by Turkey’s foreign minister to step up its airstrikes against the group. But this raises the question of whether or not Turkey will call off its war against the Kurds.

If not, America’s deal with Turkey will prove to be a Faustian bargain. Short-term operational convenience is not worth the long-term danger of destabilizing Turkey and demoralizing the Kurdish forces that have carried the bulk of the burden in fighting militants.