The best that can be achieved in this extraordinarily febrile atmosphere is for Ukraine's new leaders to display caution. Putin was flexing his muscles yesterday as he deployed Russian armour within Crimea, purportedly in defence of his Black Sea Fleet's positions. He may eventually go further and launch a military strike of some sort - but that is a high-risk gambit, particularly with so much Russian money stranded in Ukraine. For the moment, he is more likely to play a waiting game, safe in the knowledge that pro-Moscow militia in Crimea and elsewhere will continue to foment trouble.