There are lots of good, strong conservatives in SD....lots of military retirees.......they'll fight this.
The reason this happened (generic, overall, trendological reason) was explained by conservative essayist James Q. Wilson in a 1972 contribution to a book titled The New Urban Politics: Cities and the Federal Government. Wilson's essay, or chapter, was entitled "The Mayors Versus the Cities" and originally appeared in The Public Interest No. 16 in the summer of 1969. Wilson noticed that mayors during the 50's and 60's tended strongly to embrace liberal policy nostrums and side with liberal factions in controversies over policy. The reason, Wilson wrote, was that foundations run by liberal boards and Great Society federal bureaucracies run by liberals were supplying incremental and conditional dollars to municipal and other local governments, which allowed these liberal "audiences" (which Wilson defined as distinct from mere voting constituencies) to achieve enormous impact on policymaking.
So liberals didn't "win" any policy arguments during the 60's -- they just bought outcomes by leveraging their trust-funds' dollars at the margins of municipal, state, and national policy, and by parlaying Lydon Johnson's "100 days" in 1965 into a permanent advantage in political power for their fellow-travelers, by creating huge new agencies and peopling them with statist liberal activists willing to use federal money to procure local outcomes.