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The G-20 summit in Los Cabos, Mexico, proved to be far from a diplomatic triumph for U.S. President Barack Obama. Coming on the heels of previous lackluster international gatherings this year -- the Summit of the Americas in Cartagena, the NATO summit in Chicago and the G-8 meeting at Camp David -- it raises the question of whether Washington’s ability to lead in the global system has been compromised. Obama has eschewed attending the Rio+20 “Green Summit” in Rio de Janeiro, a wise choice given that the meeting is also not likely to produce any dramatic breakthroughs.