The on-going conflict between Russia and Ukraine can lead to the use of tactical nuclear weapons if either party feels threatened, and the recent tension between the two countries has raised concerns about the potential for a nuclear war.
The decision by George W. Bush to expand NATO by adding Ukraine or Georgia would not enhance the security of the US because it would threaten the relationship between US and Russia due to Putin's nationalism, which is the source of his popularity in Russia.
The bigger question beyond Ukraine is whether the United States will help its allies or choose a path of isolationism, risking its credibility and ability to deter wars. Russia being able to move deep into Europe without any buffer is a severe risk.
The US is sending weapons such as Stinger anti-aircraft missiles and Javelin anti-tank missiles to Ukraine, which the administration views as defensive weapons to help repel Russian aggression.
The Ukraine conflict could have been prevented by engaging in diplomacy, and the deal that could end the war is for Ukraine to remain a neutral state. The question is, what is Putin willing to do in terms of evading other countries?