President Trump vowed to withdraw United States troops from the Syrian border with Turkey. But such a move could harm one of America’s most loyal partners in the Middle East, the Kurds, who have been crucial to fighting the Islamic State. Guest: Eric Schmitt, who covers terrorism and national security for The New York Times. For more information on today’s episode, visit nytimes.com/thedaily.  Background coverage: President Trump’s announcement raised fears that he was giving Turkey the go-ahead to move against Kurdish forces in northern Syria.The American pullback could create a void in the region that could benefit Iran, Russia and the Islamic State.American troops have “operated between two allies: Turkey and the Kurds,” our colleagues write in a news analysis. “The problem for Washington has been that the two hate each other.”