Bush 2 fed their ego. He was what a Republican was supposed to be: A simian hick that exists to remind all the cool people how much better they are. Looking down their nose at him and telling themselves that his inferiority proved their quality was cultural bedrock to every Democrat old enough to remember 9/11.
After 16 years of nurturing their vanity, a lot of people built Trump's Certain Defeat up into a symbolic rejection of everything they didn't like about America, then they had to watch their entire worldview shatter in a single evening. I think the election hit a lot of these people harder on a much more personal level than the 9/11 attacks, and they may never really recover from the shock.
This is... more accurate than even you may realize.
The left has won. The left -had- won.
Decades of uninterrupted success, through the civil rights movements, through the Vietnam war, through the efforts for gay rights. On the cultural front, they had been winning for half a century. And their opponents? A broken collection of libertarians, stock republicans, RINOS, and evangelicals. Requiring this opposition to kow tow to a specific set of requirements to have any chance of win.
Clinton got in office, all was good, the idiot republicans tried to do an impeachment proceeding that SLAMMED them in the 1998 election, which saw the Presidents party for the first time gaining seats.
Then Bush won, in an absolutely razor tight election, and likely only because his opponent had the charisma of cardboard. Every democrat and their mother agreed, if such a terrible candidate could almost win and even win the popular vote, then any democrat going forward has to win. And sure, Bush won a second a term, but he was coasting on the events of 9/11.Everything was set... and everything worked well.
Obama won, they had massive majorities. Obviously, they were right. At this point, fill in what you yourself said. Fill in the massive idea of how they simply are the best, how all republicans are evil and stupid, and now we get to 2016.
Trump did something they never thought was possible. He united the right into a far more cohesive faction. The evangelicals had died down, but still had their beliefs and those beliefs were under threat firm the democrats. The Libertarians had seen what happens when Democrats had rule and were willing to throw themselves behind the republican regardless. The stock republicans were similarly incensed. And the RINOS, while liking the status quo, also wanted power that a republican in office would provide. For the first time in 50 years the Republican base was at peace with itself and could -fight-.
And that is when the Democrats learned something.
The Left... had lost. Not the election, yet, but lost the knowledge of HOW to fight the culture war. HOW to fight an energized opponent. 50 years of winning by default and their only losses being due to weak candidates and calamitous events. 50 years of any and all serious opposition being hamstrung from the start. 50 year, and their ability to fight had utterly atrophied.
The shock they received wasn't just the worldview crumbling. It was it crumbling AND them realizing, far too late, that they had utterly lost the ability to recreate it. That is far, far more devestating as it is not only losing the cornerstone of your worldview. It is losing it, and knowing you may never be able to reobtain it.