Soon after filing his nomination for the Congress President poll to be held on October 17, Mallikarjun Kharge resigned as the Leader of Opposition in the Rajya Sabha. He told the grand old party's working President Sonia Gandhi that he is quitting from the post in the upper house, in line with the Congress's "one person, one post" rule announced at the Udaipur Chintan Shivir. He sent a letter to Sonia Gandhi last night.