With the former president absent once again from the debate stage, the rivals aimed most of their ammunition at each other, rather than the clear frontrunner in the race.
"We don't need another mealy-mouthed politician who just tells you what she thinks you want to hear just to try to get your vote, then to get an office and to do her donors' bidding," DeSantis said.
The past 11 months have shown me the best of America is right here in Iowa.— Nikki Haley (@NikkiHaley) And my time here in Iowa has shown me that America is ready for a new conservative generational leader.If you join me in this movement, I promise our best days are yet to come. https://t.co/ioi6jyQDe7January 11, 2024
Haley touted a website her campaign has created to document what she said were dozens of DeSantis falsehoods and at one point called him "so desperate".
The two rivals have engaged in an increasingly rancorous battle ahead of Monday's first-in-the-nation Iowa caucuses, with little time left to halt Trump's march toward the nomination.
Trump had the support of 49 per cent of Republicans in a nationwide Reuters/Ipsos poll released on Wednesday, far ahead of Haley in second place with 12 per cent.
For the fifth time, Trump skipped the debate and instead was holding a Fox News town hall nearby in Des Moines, giving him a prime-time platform with a friendly television audience.
The debate was held just hours after former New Jersey Governor Chris Christie, a fierce Trump critic, announced an end to his presidential campaign after drawing little support from Republican voters.
"I would rather lose by telling the truth than lie in order to win," Christie told the audience at a town hall in Windham.
Haley and DeSantis both offered muted criticism of Trump when asked whether the volatile former president had the "character" to be president.
"I agree with a lot of his policies, but his way is not my way," Haley said.
"I don't have vengeance; I don't have vendettas; I don't take things personally."
Donald Trump skipped the Republican debate, holding a Fox News town hall in Iowa instead. (AP PHOTO)
DeSantis listed several examples of campaign promises he said Trump had not kept - having Mexico pay for a southern border wall, reducing corruption in Washington and lowering the federal debt.
He also faulted Trump for not deporting more migrants who crossed the border illegally.
Haley criticised Trump for calling January 6, 2021 - when a pro-Trump mob stormed the US Capitol - a "beautiful day" and said unequivocally that he lost the 2020 election, despite his continued false claims of voter fraud.
DeSantis was more animated and delivered sharper criticisms than in previous debates, perhaps more comfortable with only one other competitor onstage after other candidates failed to qualify for Wednesday's event.
He strove to turn Haley's foreign policy chops into a weakness, arguing that she has essentially supported an unlimited flood of aid to Ukraine.
Haley offered a lengthy answer on why helping Ukraine repel Russia's invasion ultimately strengthens US national security by preventing a broader military conflict.
She said it was a false choice to suggest that the US had to choose between helping Ukraine and Israel and securing its borders.
DeSantis, once considered Trump's top challenger, has seen his campaign struggle amid infighting, while Haley has steadily climbed in polls.
Two surveys released on Tuesday showed Haley cutting Trump's lead in the second state due to pick its Republican candidate, New Hampshire, where a primary will be held on January 23.
DeSantis is trailing in fourth place there, polling averages show, while he and Haley are essentially tied for second in Iowa.
The Republican nominee is set to face President Joe Biden in the November 5 election.
