 In 1945, Mayor William O'Dwyer picked Impellitteri to run for President of the City Council on the Tammany Hall slate.In 1945 he ran on the Democratic and American Labor Party lines, but when he was up for reelection in 1949 he ran on the Democratic Party line alone.On August 31, 1950, O'Dwyer, pursued by both federal and state investigators, was suddenly appointed by President Harry S. Truman as ambassador to Mexico, where he would be beyond the reach of officials who wanted his public testimony in several matters on which he preferred not to speak.