Defending his Sunday night decision to clear the way for a Turkish military operation against America’s Kurdish allies in northern Syria, Mr. Trump said on Monday that it was “time for us to get out” and let others “figure the situation out.” But after Republican allies condemned the move, he pivoted sharply and said he would restrain Turkey.

Quotable: “As I have stated strongly before, and just to reiterate, if Turkey does anything that I, in my great and unmatched wisdom, consider to be off limits, I will totally destroy and obliterate the Economy of Turkey (I’ve done before!),” the president wrote on Twitter .

Analysis: The Pentagon is scrambling to piece together a Syria strategy, as it is caught between a pivoting Mr. Trump, Turkey and Kurdish allies who see the announcement as abandonment.

Background: Turkey considers the Kurds a terrorist insurgency, but they’ve been the most reliable partner for the U.S. in fighting the Islamic State in a strategic part of northern Syria. The Pentagon and the State Department consider the U.S. presence a critical counterweight to Iran and Russia. Here’s how Mr. Trump’s shift could affect the region.