CARLSBAD, California (Reuters) - News Corp Chief Executive Rupert Murdoch on Wednesday predicted a Democratic landslide in the U.S. presidential election against a gloomy economic backdrop over the next 18 months. Murdoch has yet to endorse a U.S. presidential candidate but considers Barack Obama very promising, the media magnate said in an interview by two Wall Street Journal reporters at an annual conference for high-tech industry insiders. News Corp recently acquired ownership of the Journal and its parent company Dow Jones & Co. "You have got the Obama phenomenon. You have got, undoubtedly, a recession ... The average American is...