The Republican candidates for president largely avoided criticising frontrunner Donald Trump in their final debate outing in Alabama.

For almost two hours, Nikki Haley, Ron DeSantis and Vivek Ramaswamy fended off moderators’ invitations to attack him.

Only ex-New Jersey Governor Chris Christie addressed Mr Trump directly, saying he would use another term in office to persecute political rivals.

Mr Trump maintained his policy of non-attendance at the debate.

The former president has refused to take part in any of the preceding three contests and has consistently called on the Republican Party to cancel the bouts, insisting that no other candidate can overcome his double digit lead.

Despite Mr Trump’s absence, Mr Christie condemned the former president as a “dictator” during heated attacks.

His comments come after Mr Trump refused to rule out using the power of the presidency to attack political rivals during an interview with Fox News on Tuesday. He promised he would not be a dictator upon returning to office “except for day one”.

But Mr Christie failed to draw his rivals, chiefly Florida Governor Ron DeSantis, to join his broadside against Mr Trump.

Mr DeSantis, who has struggled to differentiate himself from his one-time ally and fellow Florida resident, did concede that he felt the Republican frontrunner was too old for another term as president and urged that voters support the “next generation of leaders”.

“Father time is undefeated,” Mr DeSantis said. “The idea that we are going to put somebody up there who is 80 and there is going to be no effects from that, we all know that’s not true.”

And while Ms Haley attacked Mr Trump – under whom she served as UN Ambassador – over his failure to combat China, she defended his trade record with Beijing. When asked directly about the former president’s controversial ban on immigration from seven Muslim majority countries, however, she simply said she would apply a new policy.

But Mr Christie refused to let his rivals off the hook, suggesting that their refusal to criticise Mr Trump was because “they have future aspirations”, alluding to their potential desire to join his administration.

“There’s no bigger issue in this race than Donald Trump,” Mr Christie insisted. “This is an angry, bitter man who now wants to be back as president because he wants to exact retribution on anyone who has disagreed with him.”

After Mr DeSantis refused to answer a host’s question about Mr Trump’s mental fitness for office, Mr Christie again went on the attack. It led to a lengthy shouting match between the two men.

“Guys, guys, guys,” host Megyn Kelly eventually interrupted. “No talking over each other.”

By contrast to his rivals, biotech entrepreneur Vivek Ramaswamy refused to condemn Mr Trump, instead seeking to defend the 2021 Capitol Riot and rattling off several conspiracy theories.

“Why am I the only person, on this stage at least, who can say that Jan. 6 now does look like it was an inside job?” Mr Ramaswamy said.

In a statement after the debate, a spokesperson for Mr Trump’s fundraising campaign called the debate “the biggest waste of time, money, and energy that politics has ever seen”.