“People don’t turn out to say thank you,” said Corey Lewandowski, one of the president’s top political advisers. “If you want to get people motivated, you’ve got to give them a reason to vote. Saying ‘build the wall and stop illegals from coming in and killing American citizens’ gives them an important issue.”

This fear-oriented approach reflects the degree that Mr. Trump has put his anti-immigration imprint on the Republican Party. The same raw appeals Mr. Trump made in 2016 about immigrants illegally crossing the border have not abated among most of his Republican supporters.
And his supporters say the party has little choice in an election where Democrats are eager to register their opposition to a president they despise — and that the only way to succeed in a campaign driven by turning out the party base is to focus on what grass-roots conservatives care most about.

“It’s an issue folks are emotionally attached to,” said Andy Surabian, a Republican strategist and former Trump aide. “I know that upsets some people in the donor class, but it’s the reality of where the party is.”