Because they have to. It’s decades of conservative media concealing reality finally coming to fruition.
Conservatives genuinely believe democrats are ushering in fascism, because their politicians tell them so constantly. Trump may not be pretty or even coherent, but he offers a perceived anti-establishment position in a country where corruption has clearly (to them) infected every crevice.
They see Trump as their savior. They couldn’t be further from the truth. But their media has done untold damage to them and managed to convince them over the span of about 50 years that the US is constantly on the brink of destruction.