I am not sure if the wall specifically is that important to the blue wave but you have a good point on your second paragraph. If democrats cave they will have compromised their own agenda for the next two years by validating a shutdown as a way for trump to get what he wants in spite of congress.... Add to that the political damage either side would suffer with the bases they are trying to appeal to if they budge. I think you are correct about the ball being in trump/mcconnell's court but I also get the impression democrats aren't doing enough to get public opinion to further turn on trump. Neither side has motivation to budge so far but if public opinion turns further from trump then the ones feeling the pressure would be senate republicans. And IF they take a budget proposal for a vote and it pases the senate then its over for trump... Unless trump is in the mood to fight democrats and republicans on this.
The old guard are doing their stale routine (seriously Pelosi and Schumer at that clown car podium was pretty cringey), but the new guard is slowly blooming in this swamp. Time for the old dems to give them more of a spotlight in moments like this that could sway public opinion. Unfortunately, Trump's base is invincibly ignorant, dems have no choice but to stay banded together with other dems they don't like
quite as much as
their guy, and the remaining third of the country will seemingly never give a shit about having a voice or even a passing knowledge about wtf is going on. I can't count how many times IRL I've heard the phrase "I just don't do/pay attention to politics" in the last two years. Apathy is still the worst part of american politics and this shutdown ain't changing it until tax season doesn't happen.
Unfortunately even the corrupt af Senate can and has passed budget bills (even
unanimously) as recently as today iirc, and it's all dust in the wind to McConnell. Dude is content being the congressional equivalent of kingsguard for Trump and there ain't much the rest of the country can do. Two old dudes can just burn everything down and there's little anyone can do to stop it.