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(CNN) —  

The head of House Republicans’ campaign arm sharply criticized Iowa GOP Rep. Steve King’s white nationalist rhetoric on Tuesday, just a week before King faces an unexpectedly competitive election.

Rep. Steve Stivers of Ohio, the chairman of the National Republican Congressional Committee, tweeted: “Congressman Steve King’s recent comments, actions, and retweets are completely inappropriate. We must stand up against white supremacy and hate in all forms, and I strongly condemn this behavior.”

A National Republican Congressional Committee aide said it was the growing volume of King’s remarks, rather than a specific incident, that led to the unusual rebuke.

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Responding to Stivers’ tweet with one of his own Tuesday afternoon, King didn’t directly address the chairman or the controversies over his own statements and actions. Instead, King said: “Americans, all created equal by God, with all our races, ethnicities, and national origins-legal immigrants & natural born citizens, together make up this Shining City on the Hill. These attacks are orchestrated by nasty, desperate, and dishonest fake news. Their ultimate goal is to flip the House and impeach Donald Trump. Establishment Never Trumpers are complicit.”

Stivers’ tweet came after agricultural giant Land O’ Lakes said it would no longer support King, suggesting in a statement that he is not “a positive force for good.”

King is under fire over a long series of comments he’s made criticizing diversity and immigration. King has recently retweeted a Nazi sympathizer, backed far-right politicians in foreign elections – including Faith Goldy, the white nationalist fringe candidate for Toronto mayor – and said in an interview with an Austrian publication: “What does this diversity bring that we don’t already have?”

Last year, King tweeted, “We can’t restore our civilization with somebody else’s babies.”

He has also assailed George Soros, the Jewish philanthropist and liberal donor, backing conspiracy theories that Soros is directly paying liberal protesters, including people who walked in the Women’s March.

King faces Democratic challenger J.D. Scholten in Iowa’s 4th District, a rural north-central portion of the state that includes Ames and Fort Dodge. The district voted for President Donald Trump by 27 percentage points in 2016 – but Democrats, who hope to gain at least two congressional seats in Iowa next week, see the potential for backlash against King.

Scholten is touting a left-leaning polling firm’s recent survey showing a close race, and elections handicappers have suggested the seat could be in play.

Scholten responded to Stivers’ tweet by saying, “Respect.”

“Last week I issued a challenge for at least one Republican elected official to condemn @SteveKingIA’s recent behavior. I applaud @RepSteveStivers, Chair of the NRCC. Respect. #CountryOverParty,” Scholten tweeted.

Another potential factor: Iowa eliminated straight-ticket voting in time for this year’s election – which means King won’t get votes from people who simply circle the Republican line; voters will have to affirmatively choose him.

The Sioux City Journal, which had long endorsed King, recently backed Scholten, in part citing King’s white nationalist ties and rhetoric.

The newspaper wrote: “King earlier this month put himself – and, by extension, the rest of the district – in an unflattering spotlight with a tweet in support of a candidate for mayor of Toronto described in published reports as a ‘white nationalist’ or ‘white supremacist.’ That wasn’t the first time King was tied, by his words or actions, to such intolerant ugliness.”