We won the war in Vietnam only to see the politicians lose it. Vietnam was being invaded by the North. Ukraine is being invaded by the Russians.
Ukraine is not being invaded by the Russians, but it might be soon if the West continues to meddle in Ukraine. There is a civil war raging in eastern Ukraine, pitting the Kiev government against a region that does not want to be governed by Kiev. If self determination is justified for western Ukraine, why not for the eastern oblasts?
Russia clearly has an interest in the success of its allies in eastern Ukraine, and the West perceives an interest in having eastern Ukraine remain under the rule of the new Kiev government that we helped to install. As a result there is a proxy war raging between the US/EU and Russia on Russia's southern border. Now we are upping the ante, making the situation needlessly worse and setting up another "ally" to be slaughtered when our interest turns elsewhere. As tcrlaf remarked earlier, "We have all seen THIS movie before."