Obviously they're getting unhinged because they're losing.
But the bigger issue is kind of how Lefties freak out at Fox News. Despite the fact that it's news coverage tends to be the most centrist/neutral of all the big networks. (not counting the punditry/opinion shows...) People who've lived their whole lives inside the liberal narrative freak out, seeing something centrist as reactionary right-wing.
In the same way, in terms of the broader "culture war" in America, the Left has become so used to winning on so many fronts, on the size of government, sexual mores, PC speech, welfare policy, a whole host of things... that when they get their noses rubbed in one of the few places they are losing, like over gun control, or the slow decline of unionization, you see them lose their figurative *expletive deleted*it over it.