I would just note that "...it was politically impossible" and "the Democrats were never serious in saying they wanted it" are two ways to frame the same reality. Both are true. Take your pick.
I'm not saying any democrats at the time were willing to go all in on it, but the two statements would only be two ways to frame the same reality if democrats had the ability to make unilateral decisions in the senate. They never did.
The nuclear option - changing the rules to allow majority votes to override a filibuster - has existed in potentia for a long time. The republicans have used it lately for things they consider crucial to their agenda. If the democrats wanted single payer and considered it crucial to their agenda, they could have done that. Of course neither of those "ifs" are true and we can use the lack of action to judge this.
> If the democrats wanted single payer and considered it crucial to their agenda, they could have done that.
And then watched it get blown away by next congress as soon as the GOP gained 51 seats to do whatever they want. Blowing away the fillibuster is an awful, terrible, no good idea and there is almost no legislative agenda which would validate it.
And to be clear, the GOP senators were and still are slimey bastards for basically everything they did leading up to Gorsuch. It should have never been done. They will almost certainly regret it as soon as they lose the senate.