It’s another busy day on the presidential campaign trail in Iowa.

Eleven days out from the caucuses, two of Donald J. Trump’s rivals, former Gov. Nikki Haley of South Carolina and Gov. Ron DeSantis of Florida, will participate Thursday night in back-to-back town halls to be broadcast live on CNN.

For Mr. DeSantis and Ms. Haley, who have been battling for second place, the town halls will provide prime-time opportunities for them to win over Iowans ahead of the Jan. 15 caucuses. Mr. DeSantis will go first at 9 p.m. Eastern time, followed by Ms. Haley an hour later.

Vivek Ramaswamy, the wealthy entrepreneur, is keeping up his fevered sprint across Iowa, aiming to beat the odds on Caucus Day despite his fourth-place position in state polls.

The man they are all trying to take down, Mr. Trump, won’t start appearing at Iowa events until Friday, but his surrogates are stumping on his behalf. Representative Marjorie Taylor Greene, the far-right firebrand from Georgia, and Eric Trump, a son of the former president, will hold simultaneous campaign events in different parts of Iowa Thursday night.

Mr. Trump, the overwhelming favorite of Republicans in Iowa, is regularly shown in state polls to be around or slightly below 50 percent support, with Mr. DeSantis and Ms. Haley polling below 20 percent in a virtual tie.

But Ms. Haley and Mr. DeSantis have so far spent far more money attacking each other than they have Mr. Trump, and they have both been very cautious whenever they do venture toward criticizing the former president.

Ms. Haley has focused on policy differences between her and Mr. Trump, on attack ads Mr. Trump has put out against her, and on the “chaos” that she says has followed him throughout the years. Although Mr. DeSantis has gone after Mr. Trump for making campaign promises in 2016 that he failed to keep while in office, Mr. DeSantis so far appears more comfortable attacking Ms. Haley. He has called her a liberal, a flip-flopper and the favored candidate of Wall Street, while Ms. Haley has mostly ignored him when speaking on the campaign trail.

Mr. DeSantis’s refusal to more directly criticize Mr. Trump is a version of a problem every other candidate in the race faces: Seemingly every approach to talking about Mr. Trump, whether it’s aggressively attacking him or coming to his defense, has failed to draw away significant support.

Former Gov. Chris Christie of New Jersey, who is not campaigning in Iowa and is instead staking his candidacy on the later New Hampshire primary, has most aggressively gone after Mr. Trump throughout the race. However, Republicans have so far had little appetite for that message.

Nicholas Nehamas and Jazmine Ulloa contributed reporting.