Dear Mr. President: If your word (and, by extension, that of the United States) means anything, now is the time to prove it. On Sept. 4-5, you will be attending the NATO Summit in Wales. It will offer you a unique opportunity to demonstrate to the many doubters and scoffers around the world that you, personally, and the United States, as a global superpower, still stands behinds it commitments, and its policies still carry weight.