LAS VEGAS — The Republican presidential debates have shattered ratings records by showcasing spirited exchanges between colorful and well-known candidates in a crowded field, with a combative celebrity contestant at the center of the program.

The challenge now for CNN, the host of Tuesday’s first Democratic candidate debate in the 2016 presidential race, is how to get viewers to tune in without the promise of the kind of fireworks created by Donald J. Trump and his Republican rivals.

Not only have the Democratic candidates who will take the stage at the Wynn Las Vegas been far more reluctant to attack one another than their Republican counterparts, but three of the five (those not named Hillary Rodham Clinton or Bernie Sanders) have also barely registered in the polls, which, taken together, probably makes for less of a draw.

But in interviews, CNN executives and anchors said they planned to take advantage of the smaller, more collegial field to force the Democratic candidates to address their previous statements and current positions — which are sometimes in conflict — even as they also encourage them to confront one another.