The reason Democrats aren't taking this current fascist takeover seriously is because they have always treated politics like it is a friendly intramural sport, and truly believe they will get the sportsball back for a win.
They honestly do not think Trump wants to actually murder them.
And maybe he doesn't. Maybe he's just playing the same game, but by very new rules.
But no president has ever been this completely unhinged, threatening to destroy or kill anyone who annoys him in the slightest.