Donald J. Trump raged at the leaked reports of his plan to choose Mike Pence, the governor of Indiana, as his running mate. In public, he denied having made a “final, final decision,” and postponed a planned event to unveil his choice. In a Thursday evening phone call with top aides, he asked for reassurance that Mr. Pence was really right for the job.

In conversations late into the evening, Mr. Trump repeatedly hesitated over selecting Mr. Pence, according to people briefed on the tense deliberations, who insisted on anonymity to describe the confidential talks. Even as his emissaries reassured Mr. Pence, Mr. Trump fielded a last-ditch appeal from Gov. Chris Christie of New Jersey, another finalist, who once again pressed his own case.

Advisers and family members stressed over and over to Mr. Trump that he was selecting a running mate to unite the Republican Party, not a new best friend.