What began last year as blaring political hyperbole on the right — the stuff of bold-lettered direct mail fund-raising pitches from little-known groups warning of a looming American “coup” — is now steadily drifting into the main currents of the 2018 message for Republicans.

The appeals have become a surefire way for candidates to raise small contributions from grass-roots conservatives who are devoted to Mr. Trump, veteran Republican fund-raisers say. But party strategists also believe that floating the possibility of impeachment can also act as a sort of scared-straight motivational tool for turnout. Last week, Senator Ted Cruz of Texas used his re-election kickoff rally to introduce a video featuring a faux news anchor reading would-be headlines were conservatives not to vote in November…

Advisers to the president say they have made clear to him that Republican control of the House is tenuous, and some have encouraged him to more aggressively lay out the stakes for the midterm elections, including who exactly would be in charge of key committees should Democrats retake the chamber.