evidence: But it is still worth spending time getting their views of the crisis that has engulfed the presidency of their mortal enemy Vladimir Putin. Without doubt, he is facing the most serious challenge to his authority since he first became president in 2000. [...] Another senior official, who spoke on condition he was not named, went further, suggesting that President Putin would be forced to dismiss his Defence Minister Sergei Shoigu and Chief of Staff General Valery Gerasimov, perhaps as a response to another military setback.