Marine Gen. Joseph Dunford, coming to the end of his term as chairman of the Joint Chiefs of Staff, is wrestling with one of the most vexing problems of his almost 42 years in uniform: how to save the crucial U.S. alliance with Turkey when Turkish President Recep Tayyip Erdogan seems intent on killing it.

Dunford has made a dozen visits to Ankara to try to iron out differences with Turkey over everything from protecting the Kurds in Syria to Erdogan’s increasingly cozy relations with Russia.