U.S. President Barack Obama nominates Federal Reserve Chairman Ben Bernanke (R) for a second term, in Oak Bluffs, Massachusetts on the island of Martha's Vineyard August 25, 2009. REUTERS/Jason Reed   (UNITED STATES BUSINESS POLITICS) By Ross Colvin and Patricia Zengerle
OAK BLUFFS, Mass., Aug 25 (Reuters) – U.S. President Barack Obama nominated Ben Bernanke to a second term as Federal Reserve chairman on Tuesday, entrusting him with guiding the economy out of the worst downturn since the Great Depression.