WASHINGTON (Reuters) – U.S. President Barack Obama on Saturday took aim at Democrats and Republicans alike in his final appearance headlining the star-studded White House correspondents’ dinner, but saved his sharpest barbs for Republican presidential front-runner Donald Trump. “The Republican establishment is incredulous that he’s their most likely nominee,” Obama told attendees at the black-tie event, which brought together journalists and media moguls with Hollywood stars and power brokers from Capitol Hill and beyond. “They […]