MOSCOW (Reuters) - Russia s ruling United Russia party will support President Vladimir Putin if he decides to run for a new term in office, its leader, Prime Minister Dmitry Medvedev, said on Thursday. Putin, 65, has so far kept silent on whether he plans to seek a fourth term in a presidential election due in March 2018.  Our party, and I personally, will support him in this in every possible way,  Medvedev said in an interview with Russian television channels broadcast live.  Because we believe that he is a successful president who is leading our country.  