There's a fine line between whimsical comic fantasy and strenuous silliness. Rocca, late of Comedy Central's The Daily Show, crosses that line, then keeps going. And then keeps going some more. The setup of All the Presidents' Pets that he, Mo Rocca, ''serious'' reporter, has been given a degrading assignment to cover presidential pooch Barney, only to uncover a startling secret portends yet another not-so-subtle stab at media superficiality. The wackiness flies thick and fast (intelligent animals! interspecies conspiracies! stale Matrix references!), but Rocca can't quite bring his skit-deep, shaggy-talking-dog story to heel.