By Caroline Copley BERLIN (Reuters) - Chancellor Angela Merkel's biggest contender in next year's German election campaign may not be a rival party leader but so-called "social bots" - software programmed to sway opinion on social media sites. In her first speech to parliament since announcing plans on Sunday to seek a fourth term as chancellor, Merkel called for a debate on how fake news, bots and trolls can manipulate public opinion. The role social networks Facebook and Twitter play in spreading false and malicious information has shot up Merkel's agenda after the shock election of U.S. Republican candidate Donald Trump as president.
