WASHINGTON — As Pittsburgh began burying the victims of Saturday’s synagogue massacre, the head of the House Republican campaign arm all but jettisoned Representative Steve King of Iowa from the House Republican Conference, declaring, “We must stand up against white supremacy and hate in all forms.”

The highly unusual rebuke by Representative Steve Stivers of Ohio, the chairman of the National Republican Congressional Committee, came a week before the midterm elections — but after years of incendiary and racially charged comments by Mr. King, capped in recent days by his endorsement of a white nationalist running for mayor of Toronto and a meeting with Austrian white nationalists, which he funded through a trip to visit concentration camps.

Mr. King is also locked in the toughest re-election fight of his eight-term House career.

“Congressman Steve King’s recent comments, actions, and retweets are completely inappropriate,” Mr. Stivers wrote on Twitter. “We must stand up against white supremacy and hate in all forms, and I strongly condemn this behavior.”

Mr. King fired back with a statement of his own, affirming that Americans of all races and “national origins-legal immigrants & natural born citizens” are created equal. He blamed attacks on him as “orchestrated by nasty, desperate, and dishonest fake news,” aided by complicit “Establishment Never Trumpers.”