DES MOINES — Representative Steve King, the polarizing Republican from rural Iowa with a history of racist remarks, was expecting to glide to an easy victory on Tuesday, like all of his previous eight races.

With no radio or TV ads and no debates, his largest campaign presence was a Facebook page that specializes in trolling liberals with mocking memes.

But suddenly, the overlap of the Pittsburgh synagogue shooting by a virulent anti-Semite and Mr. King’s latest inflammatory remarks, to a publication associated with neo-Nazis, have converged to add some drama to a re-election bid that once looked assured.

The head of the House Republican campaign arm, Representative Steve Stivers of Ohio, delivered an extraordinary rebuke to Mr. King this week. Mr. Stivers said recent tweets and remarks by Mr. King, including an endorsement for a Toronto mayoral candidate who had previously recited the 14-word manifesto used by neo-Nazis, were tantamount to hate speech.