Understanding the past is a prerequisite for understanding the present.
The point of the past events I cited is to illustrate that the approximate Democratic (and thus US) position used to be one of accommodation towards Russia, willingness to work with Putin, and no particular fondness for Ukraine.
At some point that changed, and the period of inflection is not hard to find. The "Russian Collusion" dirt Hillary Clinton fabricated to tar Trump in the minds of voters failed, and Clinton was left having to explain a defeat when victory was thought by most observers to be near certain. It would be uncharacteristic of her to admit her own failings. She latched onto malign Russian influence as a cause, and that subsequently became a fulcrum for leverage applied by various parties interesting in hindering the new administration. In order for all that to work, Russia and Putin had to unambiguously be villains. The cake was iced when Ukraine was dragged into US domestic politics for the first impeachment hearings. Russia is now the blackest of scoundrels, and Ukraine has had a makeover.
Once the exigencies of the moment (how can X be used against Trump?) end, Democrats will most likely return to their earlier positions. Their party is historically the one that owns trade protectionism and anti-interventionism.
An article (Mario Loyola) with some historical background that many people probably don't know, or have forgotten.