President Dmitry Medvedev of Russia says he decided not to run for a second term because Vladimir Putin is both more popular and more authoritative.
In his first interview since 24 September when Prime Minister Putin revealed their plan to swap jobs, Mr Medvedev said it did not mean next year's election result was predetermined.
He said the decision to swap their roles was taken years ago.
''Prime Minister Putin is now unquestionably the most authoritative politician in our country and ... his rating is somewhat higher,'' he said.
The BBC reports there is little doubt that Mr Putin, 58, will win the presidential poll in March.
Mr Putin has already served two terms as president. He was barred by the constitution for running for a third consecutive term in 2008.
United Russia has approved a proposal by Mr Putin that Mr Medvedev heads the party list for December's parliamentary elections and become prime minister after the presidential poll.
