Watch Winter on Fire: Ukraine's Fight for Freedom Online | Netflix

Ok, so I'm on a bus from Daegu to Osan and watched this documentary on Netflix - "Winter on Fire: Ukraine's Fight for Freedom" - and it catalyzed some thoughts, but here's a quick recap first:
Ukraine become independent from Russia. Russia attempts to steal Ukrainian elections and is caught rigging an election. Later, the same guy who was caught cheating is "legitimately" elected. Ukraine votes to join the EU, but during the actual signing of the deal, the Ukrainian signatory reverses the Ukrainian position and doesn't sign. Meanwhile, the Ukrainian President is making back-door deals with Putin in Russia. After the failure of the government to sign the document joining the EU, the people protest.
They gather in Maidan Independence Square and hold a peaceful protest. Over the course of time, things escalate between the unarmed (no firearms) protesters and the Berkut (Ukraine Special Police) over the next few weeks/months. Watch the movie, get the details.
After some violent clashes, the Ukrainian President declares a dictatorship and things escalate more. Eventually, the protesters make an ultimatum for the President to resign and the President flees the country and is given asylum in Russia by Putin.
Quickly following that, "Pro-Russian protesters" (Russia) in Eastern Ukraine seize Ukrainian territory. To this day, Russian forces are still advancing westward through the Ukraine towards Poland.
So, with the backstory out of the way, here are some questions.
Given a similar situation in the United States, at what point is violent protest the Patriotic thing to do and at what point should the military be called in?
At what point would the military fracture between supporting the protesters and using force on US civilians?
In the documentary, towards the end, the police end up using snipers to engage unarmed protesters - how does the military respond to this in the US?
In reality:
When should the United States become actively involved in defending the Ukraine against Russian aggression? There are clear threats to EU/NATO nations just west of the Ukraine (Poland).
This month, two NATO nations have partnered with the Ukraine militarily (outside of being officially NATO actions). US forces are already IN Poland.
It seems to me that THIS is the next legitimate battleground for US forces, not Syria. Syria has become a diversionary tactic by Russia to engage US and EU forces in a meaningless "war on terror" while they blatantly overthrow a legitimate government. Why isn't this a significant focus of US efforts?