While most major nations deplore Putin's aggressive response to the political upheavals in Ukraine, there seems no appetite for military intervention to oppose the moves. Germany is trying to establish some form of negotiation structure. This presents a classical case of the impotence of the UN Security Council, since Russia can use its veto power to negate any authorization for punitive action. Last summer's crisis over Syria made it abundantly clear that there is strong opposition in the UK and US for anymore military intervention in the Middle East. Since the stakes in a conflict with Russia would be considerably higher, it seems likely that the appetite for war there would be significantly smaller. Military intervention is not a political option. The Republican hawks who are rattling their pen knives know that as well. They are simply using it as an excuse to score points on Obama.
Western Governments are presently pursuing the approach of economic and diplomatic sanctions against Russia. That approach doesn't have much of a track record of being effective against much smaller and less powerful nations than Russia. There has probably been more international support for sanctions against Iran than about any other nation. While they have had an economic impact, they haven't really created a collapse. You can be sure that Putin and his ministers have done economic calculations of the consequences of their present course of action. While Russia has been moving toward greater global economic integration over the past 20 years, it has a long history of functioning in economic isolation. Europeans don't seem eager to turn off their gas in protest.
There have been large government sponsored demonstrations in Russian cities in support of the policy direction. There have been some anti-war protest, but they have been small. I doubt that this is simply a matter of government rigged public display. The Russian populace has a strong bent toward aggressive nationalism. They would like to see Russia regain a position of power on the world stage.
The conflict with Georgia in 2008 offers the best historical reference for the present situation. There was wide agreement that Russia's actions were in violation of international law. However, even the avowedly neocon Bush administration found that they had few effective options. Putin achieved an effective annexation of two Georgian provinces giving him a buffer zone. With that he packed up his tanks and went home. He is likely to wind up with a similar arrangement with the eastern provinces of Ukraine. Buffer zones have always been a core objective of Russian policy. Stalin's approach followed the course of the czars and Putin is basically using the same playbook.