boosted by his high-profile role in the National Priority Projects. Many observers were surprised when on 10 December 2007, President Putin introduced Medvedev as his preferred successor. This was staged on TV with four parties suggesting Medvedev's candidature to Putin, and Putin then giving his endorsement. The four pro-Kremlin parties were United Russia, Fair Russia, Agrarian Party of Russia and Civilian Power. United Russia held its party congress on 17 December 2007 where by secret ballot of the delegates, Medvedev was officially endorsed as their candidate in the 2008 presidential election. He formally registered his candidacy with the Central Election Commission on 20 December 2007 and said he would step down as chairman of Gazprom, since under the current laws, the president is not permitted to hold another post. His registration was formally accepted as valid by the Russian Central Election Commission on 21 January 2008. Describing his reasons for endorsing Medvedev, Putin said: 2008 presidential election Election campaign As 2 March 2008 election approached, the outgoing president, Vladimir Putin, remained the country's most popular politician. An opinion poll by Russia's independent polling organisation, the Levada Center, conducted over the period 21–24 December 2007 indicated that when presented a list of potential candidates, 79% of Russians were ready to vote for Medvedev if the election was immediately held. The other main contenders, the Communist Gennady Zyuganov and the LDPR's Vladimir Zhirinovsky both received in 9% in the same poll. Much of Putin's popularity transferred to his chosen candidate, with 42% of the survey responders saying that Medvedev's strength came from Putin's support to him. In his first speech after being endorsed, Medvedev stated that, as president, he would appoint Vladimir Putin to the post of prime minister to head the Russian government. Although constitutionally barred from a third consecutive presidential term, such a role would allow Putin to continue as an influential figure in Russian politics. Putin pledged that he would accept the position of prime minister should Medvedev be elected president. Although Putin had pledged not to change the distribution of authority between the president and prime minister, many analysts expected a shift in the center of power from the presidency to the prime minister post when Putin assumed the latter under a Medvedev presidency. Election posters portrayed the pair side by side with the slogan "Together We Win" (""). Medvedev vowed to work closely with Putin once elected.