WASHINGTON — The White House sent out a message aimed at mollifying Turkey’s president on Tuesday, suggesting that the United States was easing off its support for the Syrian Kurds. That message was quickly contradicted by the Pentagon, which said it would continue to stand by the Kurds, even as Turkey invaded their stronghold in northwestern Syria. The conflicting statements appeared to reflect an effort by the administration to balance competing pressures. Turkey, which has been furious over American support for the Kurds, is a NATO ally, while the Kurds have been critical American partners in the war against the...