SAN FRANCISCO, California (Reuters) — Bernie Sanders, on Monday (June 6) vowed to keep up the fight in what has been a protracted and increasingly antagonized primary race that has exposed deep rifts between the left-wing and the more centrist of the Democratic Party. His rival Hillary Clinton has reached the number of delegates needed to clinch the Democratic U.S. presidential nomination, according to tallies by two U.S. media outlets, the day before six states […]