In the admittedly faint hope of countering Republican stupidity, let me point you at an insightful essay in The Atlantic by Peter Beinart, "No, American Weakness Didn't Encourage Putin to Invade Ukraine". It provides historical perspective that is badly needed in order to understand Putin (and Russian leadership in general) as more than a simple power-hungry thug.
You really, really, really should read the whole thing. It's not that long. But if you need the thesis, here it is in Beinart's own words:
Geopolitically and ideologically, the West’s frontier has moved further east than almost anyone could have imagined a couple of decades ago. The bad news is that it has left the countries just beyond that frontier, the ones most eager to be connected to the West, terribly vulnerable. During the Cold War, Poland, Hungary, and Czechoslovakia shared that tragic fate. Today, Georgia and Ukraine do.Republicans treat the invasion of Ukraine as if it were a point scored in a debate against the U.S. by Russia. Their attitude not only trivializes a very serious incident, but betrays a fundamental small-mindedness about foreign policy. Beinart reminds us that where we are today represents a huge victory for the West. Even if Ukraine is drawn back tightly into Russia's orbit, the U.S. and its Cold War allies will still be very much on the "profit" side of the geopolitical ledger, if you must view things from that standpoint. Republicans shooting off their mouths about "Obama's weakness" having led to the invasion willfully ignore history. They're not just petty, but stupid.
This isn't to excuse Russia. It wasn't entitled to hold the independent states that it swallowed into the Soviet Union, or the independent states it coerced into the Warsaw Pact. Russia under Stalin and his successors created the unfriendly attitude on the part of the non-Russian populations, causing them to race into Western Europe's (and America's) arms as soon as the Russians couldn't afford to intimidate them any more. The invasion of Ukraine was immoral and unjustifiable, and I hope the Ukrainians are able to achieve their formal independence from Russia. Even better, I hope the Russians can someday get over their wounded pride, their paranoia, their chauvinism and their dreams of domination so that they won't commit acts of aggression like this any more.
We mustn't lose ourselves in the delusion that Russia's invasion of the Crimea is all about us. This misses not just Russia's and Ukraine's messy entangled history, but Russia's current strategic concerns. So Republicans, stop trying to score cheap debating points. Grow up and help the administration to address the problem.