Four decades after the fall of Saigon, and two decades after President Bill Clinton restored relations with the nation, Obama is eager to upgrade relations with an emerging power whose rapidly expanding middle class beckons as a promising market for U.S. goods and an offset to China's growing strength in the region. During his three-day stay in Vietnam, he'll make the case for stronger commercial and security ties, including approval of the 12-nation trans-Pacific trade agreement that is stalled in Congress and facing strong opposition from the 2016 presidential candidates. "Remember that leaders are lonely people," says Michael Green, senior vice president for Asia at the private Center for Strategic and International Studies. Deputy national security adviser Ben Rhodes said the Vietnam and Japan visits both reflect Obama's world view "that we can move beyond difficult and complicated histories" to find areas of common interest. [...] the U.S.