He and his newly recast team also are pledging to do more outreach to Washington Republican leaders, who have often been hostile and the target of Trump attacks, and to spend significant amounts of money to run a more conventional campaign.

Mr. Trump, in an interview, acknowledged the need for a shift. “The campaign is evolving and transitioning, and so am I,” he said. “I’ll be more effective and more disciplined.” He’s changing, he said, because “I’m not going to blow it.”