At his campaign rally in Dallas, the president brought up Turkey's agreement to temporarily pause its attacks on Kurdish-held northern Syria.
The Senate majority leader joined other Republicans who are speaking out against the president's decision to withdraw U.S. troops from Syria.
Since the flags were spotted in Kurd-controlled territory last week, Turks and Kurds have squabbled about their origins.
All the signs are, Turkey's bleeding, unresolved Kurdish issue this time comes to a boiling point.
Turkey is hoping to drive out Islamic State militants and check the advance of U.S.-backed Syrian Kurdish fighters.
Kurdish militants are suspected of having carried out the attack.