The confidant, Armstrong Williams, said on Thursday that Mr. Carson had been placing calls and “reaching out to everyone,” and planned to make the case that despite Mr. Trump’s insults in the primary race, the party needs to come together.

The outreach would include Senator Ted Cruz, Senator Marco Rubio and Jeb Bush, all of whom were frequent targets of insults from Mr. Trump during the primary campaigns.

“He can say, ‘He’s done nothing to you that he has not done worse to me,’ ” Mr. Williams said, referring to Mr. Trump’s mockery of Mr. Carson, a retired neurosurgeon, before the Iowa caucuses this year.