Even as Vladimir Putin was being ticked off by President George W. Bush in Bratislava last week for his authoritarian tendencies, cracks were spreading in the Russian president's previous aura of invincibility at home. Mikhail Kasyanov, Mr Putin's former prime minister, chose the same day - the anniversary of his sacking by the Russian president last year - to launch an attack on his former boss's policies. Russia, he said, was "on the wrong track". Its fragmented democratic opposition had to unite. Moscow newspapers, still allowed to engage in some political debate unlike Russia's state-controlled TV channels, have run analyses this week comparing Mr Kasyanov with Viktor Yushchenko, the reformist, pro- western winner of Ukraine's presidential election in December and victor over Viktor Yanukovich, the Kremlin-backed candidate.Asked if he would run for Russian president in 2008, Mr Kasyanov said: "Everything's possible." Yet his press appearance last week, ostensibly to launch a new consultancy, followed weeks of rumours in Moscow that he would run. It has left Mr Putin (or his chosen candidate, since he cannot stand for a third term without changing the constitution) facing a credible challenger from within Russia's political elite for the first time. "What's important," said Mr Kasyanov, "is not who is elected in 2008, but that whoever is should lead Russia along the path of democratic values."