"Why is Obama not responding to Russia's invasion of Ukraine?"
Russia is a nuclear armed state with a veto in the UN Security Council...what exactly do you expect him to do?
"Ukraine is a country whose people (including Russian speakers) overwhelmingly voted to become independent of Russia."
Well, yes and no. I mean the 1991 referendum did find that all of Ukraine's oblasts, special administrative cities and even the Crimean ASSR voted for independence, albeit in the case of Crimea and Sevastopol it was not a majority of eligible voters.
However it should be noted that that vote wasn't independence from Russia...it was independence from the Soviet Union. Put simply, although people assume it's the same, it really isn't.
"Why is Barack Obama doing nothing other than saying a few meaningless things?"
Because ultimately it is in no one's interests, save for the Ukrainians themselves, for the USA or NATO to go to war with Russia over Ukraine. Russia, who supplies much of the EU with the energy needed to keep their industries going, is a nuclear state and a permanent member of the UN security council.
It is not Iraq, Afghanistan or Libya...so any potential decision on Russia has to weigh carefully the fact that Russia is the regional power, and has the capacity to both punish the EU and block any UN resolutions concerning Russian actions.
Edit: I think you're a bit naïve about steps that Obama can take.
For starters, do you think there is ANY political will in the USA to folk over billions to Ukraine? And even if there was, do you see this President and this Congress being able to agree to do that?
Secondly, do you really believe an official protest would be cautionary for Russia at this point?
Thirdly, how do you know that Poland, Romania and Turkey want to be a part of US sabre rattling with Russia?
Poland has been burned by the Western betrayal before, and placing US missiles on Polish territory is unpopular in Poland.
Romania would undoubtedly be sensitive to upsetting Russia because of the fact that Russian troops never left Moldova, a former Soviet Republic populated mainly by people (Moldovans) who are ethnically, linguistically and even culturally linked to Romania.
And Turkey had it's own anti-government protests in 2013 that were not unlike the Euromaiden protests. Does Turkish Prime Minister Recep Tayyip Erdogen really want to risk sending the signal to his own detractors (who consider him an authoritarian extremist) that he supports mass public action to overthrow unpopular elected officials?