Expectations for conflict in Tuesday’s debate were at their highest point in the 2020 campaign cycle. Senators Bernie Sanders and Elizabeth Warren spent the previous two days sparring, Mr. Sanders has been fighting for a week with former Vice President Joseph R. Biden Jr., and former Mayor Pete Buttigieg of South Bend, Ind., has been in the cross hairs of Ms. Warren and Mr. Sanders for weeks.

All of these fireworks did not really materialize in the debate.

With the top four candidates in an effective tie three weeks before the caucuses, none of them saw much incentive in going on the attack.

It’s a reflection of the muddled state of the race. The candidates have all made a calculation that being the aggressor in any interpersonal conflict would only lead to increasing their unfavorable ratings — or falling down Iowa caucusgoers’ second-choice lists, a critical element because supporters of candidates who don’t receive 15 percent support will be free to back someone else.