In the 2020 debate, Joe Biden said he would veto Medicare for all*. Just this week, Hakeem Jeffries said he did not support Medicare for all and wouldn't vote for it. You already mentioned Joe Lieberman
None of what I just said implies "it's not partisan" nor does it imply "both sides are the same" -- multiple things can be true at the same time
It sure does, however, reinforce the original, plain statement: "The issue is that the people in Washington won’t make it a 'votable' decision."
*By April 8, 2020, Biden was the "presumptive Democratic nominee" -- at that time, 22 states still hadn't yet held their primary elections. As such, for those 22 states it was quite literally not a votable decision