Mr. McDaniel’s faded political fortunes point up one of the more unforeseen effects of Mr. Trump’s leadership of the Republican Party. Instead of elevating the renegade, insurgent conservatives who have vowed to challenge party leaders in Washington — candidates who are politically and temperamentally cut from the same cloth as the president — Mr. Trump has effectively shut off the oxygen to the noisiest and most fractious wing of his party…

Mr. Trump’s repositioning has led some self-styled conservative agitators to acknowledge that their bomb-throwing, anti-establishment playbook is in need of refinement.

“People are starting to realize that the anti-establishment thing is kind of a luxury we can’t afford right now,” said Stephen K. Bannon, the president’s former chief strategist who six months ago said it was his objective to see Mr. McConnell removed as the Senate Republican leader.