President Trump put a “Celebrity Apprentice” spin on his State of the Union address on Tuesday, seeding the 78-minute broadcast with surprise reveals and viral moments: a tear-stained reunion of a military family, a snubbed handshake and an impromptu bestowing of the Presidential Medal of Freedom to a guest star, the radio host Rush Limbaugh.

It was the kind of camera-ready spectacle that can translate into big ratings for afternoon talk-show hosts and prime-time reality shows.

This time, though, the Nielsen numbers did not come through.

Roughly 37.2 million Americans tuned in for Mr. Trump’s speech, Nielsen said on Wednesday, the smallest live-TV audience for a presidential address to Congress since Barack Obama’s valedictory State of the Union in 2016.

The viewership on Tuesday was a 20 percent decline from Mr. Trump’s State of the Union last year, and well below the audience for his speeches in 2017 and 2018.