WASHINGTON (Reuters) - Bernie Sanders, a democratic socialist whose progressive agenda pushed the Democratic Party sharply to the left, ended his White House campaign on Wednesday, clearing the way for a Nov. 3 election battle between former Vice President Joe Biden and Republican President Donald Trump. Sanders, a former front-runner who promised to lead a grassroots political revolution into the White House, acknowledged he no longer had a path to the nomination after a string of nominating contest losses to Biden but promised to work with the former vice president to oust Trump.