But 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.
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.
The former president had the support of 49% of Republicans in a nationwide Reuters/Ipsos poll released on Wednesday, far ahead of Haley in second place at 12%.
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 took place just hours after former New Jersey Governor Chris Christie, a fierce Trump critic, announced an end to his own 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, excoriating his rivals for failing to confront Trump more directly.
Haley and DeSantis both offered muted criticism of Trump when asked whether the volatile former president has 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."
DeSantis listed several examples of campaign promises that he said Trump did not keep: 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.
Later, Haley criticized Trump for calling Jan. 6, 2021 - when a pro-Trump mob stormed the U.S. Capitol - a "beautiful day" and said unequivocally that he lost the 2020 election, despite his continued false claims of voter fraud.
'LAST AND BEST CHANCE'
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.
"People like Nikki Haley care more about Ukraine's border than she does about our own southern border, which is wrong," said DeSantis, adding that the U.S. needs to "find a way to end" the war.
Haley offered a lengthy answer on why helping Ukraine repel Russia's invasion ultimately strengthens U.S. national security by preventing a broader military conflict. She said it was a false choice to suggest that the U.S. 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.
Haley jabbed at DeSantis regarding his candidacy, asking how he intended to run the country when he couldn't properly manage a presidential campaign.
"He spent more on private planes than on commercials to appeal to voters in Iowa," she said.
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 Jan. 23. DeSantis is trailing in fourth place there, polling averages show, while he and Haley are essentially tied for second in Iowa.
Beating each other out for second place in Iowa will be critical in their efforts to turn the race into a one-on-one matchup against Trump.
The Republican nominee is set to face President Joe Biden in the Nov. 5 election, where the latest Reuters/Ipsos polling puts Trump and Biden tied at 35%.
