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HE WAS colourless and weightless, at least politically speaking. That made Mikhail Fradkov an ideal prime minister in the Kremlin's eyes. The exact reasons for his resignation on Wednesday September 12th and replacement by a little-known tax official, Viktor Zubkov, are unclear; so far the Russian proverb, nyet faktov, tolko versii (there are no facts, only theories) is an apt one. But it is almost certainly connected with the wrangles and plots about March 2nd 2008, when Vladimir Putin must, according to the Russian constitution, step down at the end of his second term as president.

Mr Fradkov said he was resigning to give Mr Putin “full freedom of decision including staff decisions”; most observers reckon that the president had that already. Mr Putin said that he wanted a “structure of power…that better corresponds to the pre-election period and prepares the country for the period after the presidential election”. He then nominated Mr Zubkov, the little-known head of the Federal Financial Monitoring Service, to take over as the new prime minister, according to the speaker of the Duma, the lower house of parliament.

Mr Zubkov is an odd choice. Along with most of the other people running Russia, he is from St Petersburg. But unlike many of them, his career shows no obvious traces of work in the security and intelligence services. The 65-year-old worked as a collective farm boss in the 1970s and then as a Communist Party apparatchik. He was Mr Putin's deputy in the St Petersburg municipal foreign affairs department in the early 1990s; after that he became a senior official in the tax inspectorate, at the heart of relations between officialdom and Russia's rumbustious new business class.

Either of the two “first deputy prime ministers” in the government might have expected to get the job. Russian newspapers were confident that Sergei Ivanov, a hawkish ex-spy and former defence minister who is also a former colleague of Mr Putin's from his KGB days, would be elevated. He is still a leading candidate to take over the more important job of president next year. Of late he has frequently appeared in public with the president. Dmitri Medvedev, another potential candidate, was seen (or at least portrayed) as a pragmatic and more liberal-minded figure.

The resignation comes at the start of a new season in Russia's stage-managed politics. Campaigning is just beginning for elections to the Duma in December. These look set to bring a resounding win for Mr Putin's “United Russia”, with secondary roles for the tame opposition parties. Real opponents of Mr Putin will find it hard to get on the ballot, and even more difficult to get elected. They receive little coverage in the main electronic media and face tough new registration rules that make it hard for small parties, independent candidates and electoral coalitions to take part.

Few Russians seem to mind: Mr Putin's approval rating is over 80%. Many Russians say they want to vote for him again in March and hope he will continue in prominent public life. Some think that he may stay on, and that any designated successor is just camouflage. But the favourite theory is that he will become the powerful head of Russia's Security Council, in tandem with the new president. The trusted Mr Zubkov could make a suitable figurehead for that job.

So might Mr Fradkov, who is otherwise unlikely to prove more than a footnote in Russian political history. His career, involving a posting in the economics section of the Soviet embassy in Delhi in the 1970s, suggests service in the KGB. After the collapse of communism he specialised in foreign trade, and served briefly as Russia's ambassador to the European Union; in contrast to some of his predecessors in that job, he spoke two foreign languages—Spanish and English. His appointment in March 2004 as prime minister, replacing the heavyweight Mikhail Kasyanov, was then as much of a surprise as Mr Zubkov's promotion is now.

Mr Kasyanov is now an opposition politician who convincingly contrasts the reforms of his period in office, such as the introduction of Russia's highly successful flat tax, with the distinct lack of them thereafter. Mr Fradkov did manage to stay neutral between the rival clans of ex-spooks who dominate Russian politics. But he left his mark on little else. That may be Mr Zubkov's fate too.