In Republican races across the country, candidates like Mr. Blankenship are parroting the president as they try to prove to voters that they are cut from the same cloth as he is. They recite the Trump lexicon, spouting his trademark phrases and slurs like “Drain the swamp,” “Build the wall,” “rigged system,” “fake news” and “America first.”

They are channeling Mr. Trump’s belligerent and profane style of speaking, seeking to capture that essential but elusive quality that matters so much to voters these days — authenticity…

“Today the goal is linguistic,” said Frank Luntz, a Republican strategist who specializes in the words and messages that candidates use. “We are no longer rewarding policy; we are rewarding rhetoric.”

“On a personal level,” Mr. Luntz added, “it sickens me.”