Conservatives have given up trying to win on the issues because, well, they can't. Boiled down, their only idea is installing a patriarchal Christian theocracy in a country with demographics going the opposite direction.
So they have one move: make things worse. People turn to the right when threatened or scared, so the path to victory is to drive the country into the ditch. Part of that is relentlessly repeating that everything is going to hell until people hear it often enough to believe it.
It's a destructive nihilistic disaster in the making, but they'd rather bring the country down than lose it.
It sounds weird for the self-proclaimed party of patriotism, but there's no contradiction: anybody who's been paying attention knows that they don't love America in general, only the version they own. If it changes, it's not America anymore, so blowing it up isn't unpatriotic.
To head off any cries of conspiracy theory, they haven't been particularly shy about any of this.