Republican voters put him up there. Because the story of the GOP since 2008 has been one of a continued and sustained descent into the rhetoric of race baiting and conspiracy theories. Because instead of working towards bipartisanship, Tea Partiers like Ted Cruz went to Washington with the express purpose of shutting down the legislature, and shutting down the government.
And it's all well and good for Republicans to say they don't support what Donald Trump is saying or doing, but at some point you have to own your candidate. You voted for him, as a party. You share the blame for his actions and words.