I've seen this movie before, and it doesn't end well.
Russia has begun military exercises, involving more than 8,000 troops, close to the border with Ukraine. The defence ministry in Moscow confirmed that artillery such as rocket launchers and anti-tank weapons would also be involved in the exercises.
I'm reminded of teenaged games of Risk, where a foe piles a big stack of troops on a border country; "Ooooh, threat...of...war." However, this isn't Risk, since there is no Russia in Risk.
We've let the annexation of Crimea slide other than taunting Putin an second time and casting sanctions in his general direction. However, that's not as wimpy as is seems, for a second Crimean War would be very messy given that it would require an amphibious landing in the enemy's home turf. It would leave little of Crimea left to the winner (which might not be our side, depending on how badly each side wants it) and might result in WW3. Add to that the concept that the area is majority Russian and was part of Russia prior to its shift to Ukraine in the 1950s (thus a potential pain to manage if we did win that war), and there is little other than "we can't just let them do that" to justify such actions at the moment.
As per the vote on Sunday... you expect it to fail? With Russia troops on the ground, no independent observation and room for all kinds of dirty tricks up to and including reporting the results you want to report, the only question will be how big a number gets reported. The bigger the number, the higher the middle-digit is held in the air to the rest of the world by Putin.
Going after the rest of Ukraine... that's another matter. There, we have some supply lines via Poland, which is a NATO member now. Poland, having lived under the Soviet thumb for the better part of a half-century, doesn't want to go back and doesn't want to see Ukraine go back, for they'd be high on Putin's shopping list if they're allowed to grab the eastern Ukraine.
While the US and the rest of NATO wouldn't be honor bound to roll with the Poles if they decided to aid Ukraine, they would if such actions saw Russia attack Polish soil in reply to active Polish aid. That could easily back us into WW3 and the unpacking of battle scenarios we thought went out the window a quarter century ago with the end of the Cold War.
Tom Clancy's spinning in his grave, kicking himself for not writing this script. Unfortunately, we have to live this one rather than see the movie.