Long known for his improvised and volatile stage performances, former President Donald J. Trump now tends to finish his rallies on a solemn note.

Soft, reflective music fills the venue as a hush falls over the crowd. Mr. Trump’s tone turns reverent and somber, prompting some supporters to bow their heads or close their eyes. Others raise open palms in the air or murmur as if in prayer.

In this moment, Mr. Trump’s audience is his congregation, and the former president their pastor as he delivers a roughly 15-minute finale that evokes an evangelical altar call, the emotional tradition that concludes some Christian services in which attendees come forward to commit to their savior.

“The great silent majority is rising like never before and under our leadership,” he recites from a teleprompter in a typical version of the script. “We will pray to God for our strength and for our liberty. We will pray for God and we will pray with God. We are one movement, one people, one family and one glorious nation under God.”

The meditative ritual might […]