WASHINGTON — As President Trump doubles down on a re-election approach of stoking fear of immigrants, he is once again elevating a voice of validation — and many say racism — that he discovered during his last presidential campaign.

That voice is Katie Hopkins, a far-right British commentator who has made denunciations of migrants and Muslims — and defenses of Mr. Trump 

On Saturday morning, Mr. Trump invoked Ms. Hopkins shortly before a mass shooting that killed 22 in El Paso, where the suspect wrote an anti-immigrant manifesto that echoed Mr. Trump’s inflammatory language about migrants.

The president, at his golf club in Bedminster, N.J., shared a tweet from Ms. Hopkins condemning London’s mayor, Sadiq Khan, over the city’s crime rate. Mr. Trump has feuded with Mr. Khan since 2016 when Mr. Khan criticized his remarks about Islam.

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“The nipple-height Mayor of Londonistan has NEVER been so unpopular,” Ms. Hopkins tweeted. “He has MINUS approval ratings because we are stab-city. London deserves better. Get Khan Out.”

On Monday, facing public pressure to address the racism behind the El Paso shooting, Mr. Trump spoke critically of white supremacism, in remarks drafted primarily by an adviser, Stephen Miller. But it is often Mr. Trump’s Twitter feed that carries his authentic voice.

Mr. Trump has a history of promoting inflammatory far-right opinions, including those of white nationalists, conspiracy theorists, and critics of Islam. Still, the president’s embrace of Ms. Hopkins, amid a flurry of other news stories, has received little attention, something that has concerned some advocates of immigration reform.

“There is no debate on what sort of person Katie Hopkins is,” said Todd Schulte, the president of the group FWD.us. “The president should have stopped using his platform to spread her ideology long ago. He has not; that tells people all they need to know.”

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