Very expensive business keeping 100,000 troops on station and ready to go. Let alone prepare an area with bridging equipment, tanks and all the logistical supplies needed for a war. Sooner or late the treasury will start weeping at these costs and the men will want to go home to see their families.
Mr Putin has been playing this game for months though, Troops positioned to both expand Crimea to attach to a Greater Russia and conquer the Donbass region with its big cities and heavy industry. More worryingly, the maskirovka is in full swing - stories of the CIA prepping chemical weapons in Ukraine for example.
The price would be high though, Ukraine will fight on home territory, they don't much like the Russians and the russian troops - who knows how they will do, many are just conscripts. Russian equipment is both good on paper and poor in performance.
But the West will not defend Ukraine. Some sanctions yes, severe ones even, but Germany still need Russia's gas. Mr P is currently turning this on an off in a display of his power. How Merkel, so lauded like Obama, has left a gaping strategic wound.
Can Europe survive without Russian gas? In the short term, no, not without power cuts which will visit the UK too. In the long term yes. Plenty in the tank of Uncle Sam that can be shipped (at a price!) to Europe in a war-footing scenario. Equally though, the yanks might let Europe squirm a bit, having told Germany not to do this for decades, they will be very keen on an 'I told you so' moment.
For Mr P, the upside is an odd one. yes an expanded Russia but international oblivion for 20 years. Long-term, less dependency on her gas which is the only valuable product they have. Maybe he plans to sell it all to China, who are less concerned about CO2 emissions anyway.
Maybe it is all an elaborate ruse to get Ukraine to say it will never sign up to Nato and to get Nord-Stream2 approved which will in turn impoverish Ukraine suitably.
But the troops are there now, the stand-off has a time limit.