By Humeyra Pamuk WASHINGTON, June 24 (Reuters) - NATO Secretary-General Mark Rutte sought to calm tensions with President Donald Trump at the White House on Wednesday, using a mix of flattery and gentle pushback to argue that examples of allies' reluctance to support the U.S. war with Iran were "isolated cases." The NATO chief is visiting Washington to try to ease strains over the Iran war and U.S. threats to draw down troops in Europe ahead of a pivotal NATO leaders' summit in July in Ankara.