A senior Russian politician has quit the state's ruling party three months ahead of a crucial parliamentary vote in December. Igor Isakov has withdrawn his membership from United Russia, his spokesman said on Tuesday. Isakov was a south Krasnodar Region deputy with the pro-Kremlin party, which has a ruling majority in parliament and is headed by Prime Minister Vladimir Putin. Three months ago, Joaquim Crima, the first black man ever to be elected to public office in Russia, quit Putin's party, claiming that it acted as a brake on the country's rocky road to democratization. A source in the Krasnodar administration told RIA Novosti Isakov might join the Russian metals tycoon Mikhail Prokhorov's Right Cause party, which supports President Dmitry Medvedev, at a time when there is growing speculation that Putin might run again for presidency. Putin, who served two terms as president before becoming prime minister in 2008, is widely tipped to stand again when Medvedev's current term expires next year. Recently, he has been trying to shift attention away from United Russia, whose approval rating has sunk below 50 percent for the first time since 2007. Instead, the emphasis has been on the All-Russia People's Front, a coalition launched by Putin in May. Analysts say the group, which even its members have difficulty defining, is designed to get Putin back into the Kremlin. So far, hundreds of trade unions and social organizations have rallied to the front.