The Democrat Attack Machine is a 1984
-esque Goldstein Conspiracy assumed to exist by ideological Republicans who believe everyone who isn't an ideological Republican is either stupid or evil.
The existence of a conspiracy fills the human need to have something to struggle against. It doesn't matter if the Machine exists or doesn't exist, since it offers a banner to rally around for Republicans to divide "us" (the faithful) from "them" (the enemy who must be destroyed)
The "Democrat Attack Machine" is (apparently) made up of every American who is not as rabidly pro-Republican as some Republicans would like.