There are strange and worrying things happening in Russian occupied Crimea. The Russian Military has been building up its forces on the de facto border between Russian and native controlled Ukraine. There has also been a blocking of ISPs in the border area apparently by 'executive order' and military vehicles and equipment has been recorded travelling from Russia to Crimea earlier this week over the Straits of Kerch. Anyone who witnessed the events of spring 2014 that led to the Russian occupation of parts of Ukraine would already be uneasy at these developments. This disquiet would only be increased by Russian claims to have engaged Ukrainian Special Forces who had breached Russian lines into Crimea which Ukraine denies.
Given that the Putin regime has what can be called an unconventional and flexible relationship with the truth, behaving dishonestly about everything from geopolitics to sport, it's not unreasonable to be concerned that the stage has been set for another Russia military infringement of Ukrainian sovereignty. This is a view that is given further weight by Putin's former Ukraine based lackey-cum-warlord and now critic Igor 'Strelkov' Girkin claiming this is exactly the case. There have been some arguments that this is merely to set the scene for a purge in Crimea of pro-Ukraine elements, though if this is so, then one must question the increased military movement from Russia to Crimea when there are probably already enough troops in the peninsula to carry out a purge unaided.
This activity in Crimea comes at a time where there is fear over Russian military advances and claims in the Times that the Russian military has developed an advantage over British forces in technology and tactics. Although fatal imperial overstretch coming from overconfidence and hubris is a possibility with any superpower, it's probable though not certain that that the Baltic States and other NATO powers will be safe for now. If Russia did openly invade Ukraine, the militarily complications arising from such an endeavour combined with Russian involvement in a worsening situation in Syria, would make a war with NATO practically impossible.
Make no mistake, Ukraine will be no walkover for Russia in the same way Iraq or Afghanistan weren't for America. According to Newsweek in November 2014, over four thousand Russian soldiers are believed to have died (and had their deaths covered up) in Ukraine contesting the southern halves of two of Ukraine's twenty-four oblasts. Fighting to conquer the remaining twenty-two oblasts, through the urban landscapes of the Central and East and the forests and mountains of the West would likely lead to tens of thousands of deaths, rivalling the death tolls of the Russian Federation in Chechnya and the Soviet Union in Afghanistan.
This before the guerrilla warfare stage begins though, as it is one thing to defeat a country's army, but quite another to defeat its people. Russia in its many guises over the centuries has had to deal with insurgencies and uprisings from Poland and Finland in the West to Central Asia in the East. The usual Russian way of counterinsurgency is to defeat through massacre and atrocity, but what might work in the small and isolated rebel province of Chechnya is unlikely to work among forty-two million Ukrainians with a memory of independence, extensive links to the outside world and ready access to arms and explosives. It's not the initial invasion that is the hardest aspect as America found out in Iraq, but maintaining the peace.
If Russia were to escalate its aggression in Ukraine, it would be an intense embarrassment and humiliation for Donald Trump who pushed for pro-Russia, anti-Ukraine changes to be made to the Republican Party policy platform. Trump looks at three months out to be extremely unlikely to win the election, so one of the deciding factors for the timing would be to start a conflict before Hillary Clinton, who has the exact opposite views on Russia and Ukraine to Trump, inevitably wins. The reason for this is because Clinton has the exact opposite views on Russia and Ukraine, and would take a stronger line on the matter than the current Obama administration.
Ultimately, whether this is another case of sabre-rattling by the Russians or something more sinister, it remains the truth that an invasion of Ukraine would be so complex and costly it would tie up Russia for years, making any interference in the Baltic States by Putin to be quixotic to the extent that along with his involvement in Ukraine and Syria, it may prove instantly fatal to his regime.