Florida Governor Ron DeSantis and former United Nations ambassador Nikki Haley are squaring off Wednesday night in a final debate ahead of next week’s first Republican presidential nominating caucuses in the farm state of Iowa, but the front-runner in the contest, former President Donald Trump, is again refusing to debate.

Polls in the U.S. heartland state show Trump with a commanding 30-to-40-percentage-point lead over DeSantis and Haley. That has given Trump leeway to skip their faceoff on CNN and instead appear on Fox News at a voters’ townhall to answer their questions without being challenged directly on a debate stage by his political rivals.

The Monday caucuses, in which voters cast ballots at firehouses, schools and community centers, are the kickoff for the 2024 Republican presidential nomination contest, followed by weeks of more caucuses and party primary elections throughout the country.

But polling shows Trump, who is facing an unprecedented 91 criminal charges across four indictments, with such a substantial advantage among Republican voters over DeSantis, Haley, former New Jersey Governor Chris Christie and entrepreneur Vivek Ramaswamy, that his campaign has predicted he could clinch the party’s nomination by the end of March. Neither Christie nor Ramaswamy have polled high enough to qualify for the CNN debate.

With Trump’s huge polling lead in Iowa, the DeSantis-Haley faceoff has effectively become a contest between the two to become Trump’s main challenger as the national nominating contest moves to the northeastern state of New Hampshire for a January 23 primary.

Trump also leads in New Hampshire, polls show, but with Haley — who served as Trump’s ambassador to the U.N. and was previously governor of South Carolina — gaining ground compared to voter surveys several months ago.

Over months of campaigning for the Republican nomination, both DeSantis and Haley have been reluctant to take on Trump with gusto for fear of alienating his supporters.

Both, however, have assailed Trump for skipping all the presidential debates in the last few months. More recently, they have also blamed Trump for failing to finish the wall he promised to build along the Mexican border to curb migration, for allowing the country’s national debt to balloon during his White House tenure and to clearly define his position on limiting abortions in the U.S.

  debate, desantis, haley, iowa, trump