Fifty years ago on Tuesday, communist forces launched the assaults across South Vietnam known as the Tet Offensive.  The offensive marked an inflection point in the Vietnam War.  President Lyndon Johnson denied a request the following month from his military commander in Vietnam, William Westmoreland, for 206,000 more U.S. troops on top of the more than half a million that already were there after years of escalation.  Johnson turned to diplomacy in a search for a peace settlement and announced he would not run for re-election.  The following year he turned over power to his successor, Richard Nixon, who presided over four more years of war and a gradual de-escalation until a peace agreement was signed in January 1973.