DES MOINES — Six and a half months ago, with the Iowa caucuses a speck in the distance, roughly 18 million Americans paused their evenings to watch a group of Democratic presidential candidates debate onstage in Miami, a record audience for a televised Democratic matchup.

The caucuses are now less than three weeks away. The field has narrowed, the first votes are set to be cast. And on Tuesday, 13.5 million people tuned in — for a prime-time version of “Jeopardy!” on ABC.

As for the Democratic debate in Iowa, the final gathering of contenders before voters start weighing in? About 7.3 million people watched live on CNN, according to Nielsen.

It was a respectable audience, beating almost every other network in its time slot, but still down from past highs. Viewership fell short of a CNN debate in October, which attracted 8.3 million viewers, and an ABC debate in September, when 14 million tuned in.