Trump's Brussels speech to the heads of state of our most valued allies in NATO did great damage to American diplomacy. He was to speak to dedicate a monument to Article 5 and the Sept. 11 attack. Article 5 states that an attack against any single member of the alliance is an attack against all of them. The only time in the alliance's 68-year history when that clause was invoked was after 9/11. Our allies rallied to support the United States; 1,036 European and Canadian soldiers lost their lives fighting America's war in Afghanistan. Trump made no mention of their sacrifices, nor did he reaffirm America's commitment to honor NATO's mutual defense treaty. Instead, he harangued his audience about their failure to pay their fair share and for allowing people escaping from the madness in Syria to take asylum inside their borders. The Brookings Institute's Thomas Wright, writing in The Atlantic magazine, said, "Trump's failure to personally endorse Article 5 may come to be one of the greatest diplomatic blunders made by an American president since World War II." Our prior commitments to mutual defense among NATO member states has been the greatest single deterrent to Soviet (and now, Russian) military action against Europe. Trump is on record as saying "NATO is obsolete." He's also on record for saying that it is no longer obsolete. Diplomacy is not a guessing game. People need to know what America's intentions are, where our nation's red lines are, and what the consequences of crossing those lines are. He would do well to remember that fact.