WASHINGTON (Reuters) – For the second time in less than two years, a U.S. Senate race in Georgia will go to a runoff, this time between incumbent Democrat Raphael Warnock and his Donald Trump-backed challenger Herschel Walker. Unlike the last time, the Dec. 6 vote will not determine whether President Joe Biden’s Democrats hold control of the Senate, where they have already secured enough seats to maintain their razor-thin majority. But there is still a lot at stake for both parties: DIMINISHING MAVERICK DEMOCRATS Democrats held the narrowest possible majority for the past two years in the 50-5…