Well, I don't say exactly that the Democrats "forced" Republicans into moving further to the right. Democratic triangulation, the two-party system, and Republican Machiavellianism and sociopathy together did so.
Of course Republicans had a choice, but their most villainous option, or to use the euphemism, their "politically smart option" was to avoid competing with Democrats for the noncrazy, moderate vote and to corner the market on the trolls and troglodytes, as it were.
I certainly blame Republicans for what I've called numerous times their flat-out evil (psychopathy). I've written numerous articles about the magnitude of Republican wrongdoing and corruption. But I also look for surprising and ironic truths, and I think I've found one here: Democrats had a hand in this debasement of the US government and the political discourse.