But an organization that can fend off such a landslide does not appear in the offing. In a departure from every modern White House, Mr. Trump himself largely dictates whom to back and how to support his preferred candidates. Even before tensions between the president and Senate Republicans flared back up over Mr. Moore’s candidacy, there was little regular communication between West Wing officials and Republicans overseeing the 2018 races, Republicans say.

The scheduled meetings between the White House, the Republican National Committee and the House and Senate campaign committees stopped months ago. Congressional officials find it difficult to get presidential signoffs for even small requests like using Mr. Trump’s name in direct-mail appeals, according to party officials. And less than a month until the election year begins, he has not scheduled a single fund-raiser for a candidate running for the House, Senate or governor…

Some top strategists involved with the midterm elections, including officials with the pre-eminent Republican Senate “super PAC,” say they have yet to set foot in the White House for political planning sessions. A Trump adviser insisted that meetings were taking place, but said that for legal reasons, they were not happening at the White House.