*Who's* national security is undermined?
Really? Show me the OPLAN (Operations Plan) of a plausible scenario, with a Commander's Intent, Mission, Purpose, End State, and Scheme of Maneuver, where the Russian military would engage in a conventional attack against the continental US. Otherwise this statement is false. This is why I rank Woodrow Wilson as the worst US President of All Time: He really put into practice this idea that "Europe's problems are America's problems", and it's saturated the minds of Americans ever since.
However, if Russia has cause to believe that the USA will not honor its commitments to NATO, that could tempt Russia to try to "take back" one or more of the East European countries it lost after the cold war (similar to the way it "took back" part of the Ukraine in 2014).
The Russians are deeply pragmatic. What would they have to gain by annexing the Baltic states? The Russian minorities are small and their economies, while decently developed, are small in the aggregate. They can only expect unplanned 2nd and 3rd-order effects of an invasion, and probably a costly insurgency, not to mention souring their relationship with the rest of Europe. Europe is still their primary customer for natural gas exports. Even in the shoddy condition of their military in the late 90's/early 00's, there were no indications they were even *thinking* of such a course of action. It's only been the constant expansion of NATO right up to their border, combined with the US's deployment of Anti-Ballistic Missiles on their doorstep, that has led to a belligerent reaction.
Russia's nuclear arsenal is the primary tool for assuring national survival, and US attempts to undermine the MAD balance are rightly taken as an extreme national security threat. Obama won't even discuss the ABM issue with Putin. ( http://www.zerohedge.com/news/... ) The last time someone built a military alliance up to their Western doorstep, it cost the Russians 20 million+ lives to rectify the situation. Do you think they are willing to give us the benefit of the doubt and risk repeating such a nightmare?
Re: Ukraine. Sevastopol is Russia's only warm-water port, which they had been leasing from Ukraine. It's a vital part of their national security strategy. Given the possibility of Ukraine slipping entirely into NATO/the EU, could they really risk hoping to maintain their base lease with a government totally hostile to them possibly in power? No. So they snatched up the whole peninsula, and with virtually-no casualties (theirs OR Ukrainian) in the process. The insurgency in the separatist eastern states is meant to a) keep some semblance of a buffer between Russia's official land border and the obviously-less-than-friendly NATO military alliance b) keep Ukraine as a whole unstable enough to make full NATO/EU integration unlikely, and a forward-deployment of NATO troops in the east even less so. It's entirely reactionary to the US's attempt to move Ukraine out of Russia's orbit (here's where Nuland affirms her quote about $5 billion spent in Ukraine "to promote democracy": http://iipdigital.usembassy.go... and here is her caught on tape playing kingmaker after the Maidan riots: https://youtu.be/r5n8UbJ8jsk ).
Russia was content with the status quo vis-a-vis Ukraine, for the most part. How would the US react if China quietly funded NGOs to "promote Communism" in Mexico, culminating in the Mexican government being overthrown and replaced with a single-party Communist state? How would the US react if the Chinese built anti-ballistic missiles in *Canada* to "protect against rogue Iranian warheads" (Note: this is the actual BS argument the US gave for putting missile sites in *POLAND*).
So let's imagine that Trump is elected, and then Russia bets that Trump won't bother to defend, say, Lithuania, and so Russia sends in their troops to "reclaim" Lithuania.
Again, this is my point: you are just taking it as a given that Russia will conduct an offensive operation to seize territory in the absence of provocation from the West. I'm saying there is no hard evidence to support this assertion. They have little to gain by doing so. In 2008 they could have easily occupied and annexed Georgia, if they wanted to. Russian forces had shattered the Georgian defensive lines and could have pushed to take the capital of Tblisi. The US and NATO were tied down in Iraq and Afghanistan, the US had threadbare forces in Europe, and so were in even less of a position to counter-attack than now. And yet the Russians didn't gobble the country up.
*sigh* One of the basic principles of warfare and military planning is understanding your enemy. To plan effectively you need to think about what the enemy might do, and *WHY*. In the US military, at the especially at the tactical level, we call this "turning the map around." In other words, looking at the battlefield from the enemy's perspective. Think about what they want to accomplish and how they could best achieve their objectives. Only then can you adequately develop a plan to counter their moves.
But normal people either don't understand this, or simply refuse to contemplate it. Everyone is just thinking "Well, I read on the Internet that The Other Guys are maniacal, mustache-twirling, warmongering villains, so all of our planning should reflect this basic fundamental truth." It's quite frustrating to witness.
Now what happens? Either Trump doesn't respond, in which case NATO is exposed a paper tiger, and Russia (and potentially others) now feel free to invade more countries when they want to;
So you want to continue playing world police? When are you enlisting? Can I put you on point during patrol, so you can eat the first Russian bullet? Or you just want "The other 1%" (aka the portion of the US population in the military) to keep dying to assuage your moral angst at what you perceive as injustices on the far side of the globe?