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.
“We must stand up against white supremacy and hate in all forms, and I strongly condemn this behavior,” Mr. Stivers wrote.
In Des Moines on Thursday, Mr. King responded angrily when accused of sharing the same ideology as the Pittsburgh shooter, and he demanded that the man who made the suggestion be ejected from a candidate forum.
In an acknowledgment of the heat Mr. King is feeling, his campaign released its first TV advertisement Friday. (It turned out to be an expression of heartland pride and optimism recycled from his 2014 campaign.)
A public poll on Monday showed Mr. King leading his opponent, J.D. Scholten, by a single point. After news of the survey popped up on social media, money poured in to Mr. Scholten from around the country: $641,000 in 48 hours, his campaign said, enough to launch a 90-second TV ad of his own, featuring farmers, mothers and others who the campaign says are former King supporters.
Three large agriculture businesses — Land O’Lakes, Purina and Smithfield — announced they would no longer support Mr. King because his conduct did not represent their values. AT&T announced Friday that the employees who manage disbursements from its political action committee have determined that it will not make future contributions to him.
Douglas Burns, an owner of The Carroll Daily Times Herald and other newspapers in Mr. King’s deeply conservative district, which President Trump won by 27 points, said the Republican base was still with Mr. King, who remains the favorite to win. But Mr. Scholten was his first Democratic challenger not easily caricatured as a carpetbagger or a liberal. Mr. Scholten, 38, is a fifth-generation Iowan and former professional baseball player who is running largely on his biography, not ideology.
“I think Scholten’s strength is that he is an acceptable place for potentially a lot of Republicans or Republican-leaning independents to park a discontented vote,” Mr. Burns said.
He added that Mr. King has been running “the laziest campaign” he has seen. “King is a natural political animal. He’d maul Scholten in a debate, but he is just ignoring him. I don’t understand why.”
In contrast to the often elusive Mr. King, Mr. Scholten has crisscrossed the 39-county district in an RV named the Sioux City Sue, for the Gene Autry song, sleeping overnight in Walmart parking lots, while accusing the incumbent of ignoring constituents to pick fights on behalf of white nationalists.
“People have been frustrated with King for years but they haven’t had somebody else they could trust,’’ said Mr. Scholten, calling from his RV on Friday. “That’s why we made such an effort of getting out there to the people.” He is stopping in downtowns to encounter voters of both parties rather than just holding town halls that attract supporters.
The issues he talks about are mainly the high cost of health care and making a farm economy work for young people who keep moving away.
“Every time I fill up this RV with gas there’s usually a donation box for someone who just got sick or in an accident,” he said. “We live in the wealthiest country in the world and people have to beg to pay for their medical expenses.’’
In the past, Iowans in the Fourth District rolled their eyes, or simply ignored Mr. King’s controversial statements about undocumented immigrants or Muslims that attract national outrage. He was a Republican whose views on abortion, taxes and gun rights were in step with the voters in northwest Iowa, the state’s most conservative region. Two years ago, he was re-elected to an eighth term by 22 percentage points.
Senator Charles E. Grassley, Iowa’s senior Republican, declined to discuss Mr. King on Friday at a campaign stop for a different House Republican, Representative David Young. “I don’t want to give you any words that would detract from the importance of re-electing Young,” he said.
Nancy Trapolino, a 34-year-old mother of two from Arcadia, Iowa, who works in a family business that manufactures farm machinery, said she was likely to vote for Mr. King to keep the House in Republican hands. She approves of the tax cut passed last year and other Republican priorities.
“I haven’t found anybody running against Steve King that’s given me much hope,” she said. “I do think having a Republican Congress is going to be important for achieving some of the goals that they have.”
Asked about his remarks supporting white nationalists, she said: “I can’t support the racist remarks Steve King makes. It makes me upset.”
Mr. King’s most fervent supporters have in the past accepted his denials that he is a racist and agreed with him that news media distorts his remarks.
But his latest comments and actions come at a time when the country’s nerves are newly sensitive to hate speech, after the Pittsburgh massacre and Mr. Trump’s escalation of heated rhetoric about the caravan of Central Americans headed toward the United States, and his misleading online ad about an undocumented immigrant bragging about killing police officers.
Recently, Mr. King endorsed a white nationalist running for mayor of Toronto. In the interview he gave to the far-right publication, in Austria, he linked the wealthy Democratic donor George Soros to a conspiracy theory known as “the great replacement,” which accuses elite groups of seeking to replace white populations with immigrants.
He also argued that diversity does not strengthen American society. “What does this diversity bring that we don’t already have?” he said. “Mexican food, Chinese food, those things, well, that’s fine, but what does it bring that we don’t have that is worth the price?”
The remarks came after a five-day visit he made to Holocaust sites funded by a nonprofit group that educates lawmakers about Nazi genocide.
In his Des Moines appearance on Thursday, Mr. King vehemently rejected a connection between his words and actions and the anti-Semitic ideology of the Pittsburgh gunman.
Saying he has “stood with Israel all along,” he asked organizers to remove the man who suggested a connection to the gunman, adding, “I’m not listening to another word from you.”
“You’re done; we don’t play these games here in Iowa,” he said.
On Friday, Mr. Scholten said his internal polls showed him further behind Mr. King than the survey showing a one-point race, but he is happy the attention will drive up his name recognition, which has been a challenge of his campaign.
“We’re just saying there is a need in the Fourth District for a new moral leadership, one that rejects white supremacy and racism,” he said.