The Republican presidential candidate has a private meeting with the group scheduled on Monday before they make their offer of support official, according to his campaign. The endorsement comes as Mr. Trump has faced criticism for stoking racial tension and has seen his support among evangelical Christians start to waver in polls as voters consider Senator Ted Cruz of Texas and Ben Carson.

That tension was evident this week after an activist for the group Black Lives Matter was beaten at a Trump campaign rally, and the billionaire developer said that perhaps the activist deserved to be roughed up. Mr. Trump also angered some when he sent a Twitter message that appeared to play down the ...