WASHINGTON - Olympic gold medalists Michael Phelps and Nastia Liukin guest star in the final holiday doggie video from the White House. In the “Barney Cam” Christmas greeting, the first family’s Scottish terrier scampers amid the White House’s red, white and blue holiday decorations before retiring for a nap and imagining himself as an athlete. Barney is shown in cutout animation as an Olympic vaulter, swimmer and synchronized diver with fellow terrier Miss Beazley, both in red swimsuits. He also dreams of sinking the final putt to secure the Ryder Cup, with the entire U.S. Ryder Cup team chanting “Barney,...