Leading Republican presidential contenders Marco Rubio and Ted Cruz took aim at Donald Trump in their final debate before next week's Super Tuesday, when 12 states and a territory hold crucial primaries and caucus votes.
The attacks on Trump on Thursday came as another Republican senator and former presidential candidate, Lindsey Graham, described the billionaire businessman as "a nut job" who would likely win the party's presidential nomination, but would lose November's election.
Graham told the AP news agency Trump was "just generally a loser as a person and a candidate".
"You can't nominate a nut job and lose and expect it doesn't have consequences," Graham said.
Rubio, Cruz and Trump were among five contenders taking part in the live televised debate in Houston, Texas on Thursday.
Ohio Governor John Kasich and retired neurosurgeon Ben Carson remain in the race.
The debate degenerated into a shouting match with moderators trying to bring the candidates back in line.
Rubio blasted Trump for hiring Polish workers to build his landmark Trump Tower in New York, even as the real estate mogul has made his central campaign promise the construction of a wall along the Mexican border to keep out undocumented migrants.
"I've hired tens of thousands of people over my lifetime - tens of thousands," Trump retorted.
"Many from other countries instead of hiring Americans," Rubio replied.
Rubio also said Trump would be selling watches in Manhattan if he hadn't inherited his father's money.
Cruz also attacked Trump for allegedly hiring migrants without papers, failing to release his tax returns, and shifting his positions on a variety of issues.
All three leading candidates said they would deport more than 11 million undocumented migrants if elected to the presidency.
READ MORE: US debate: Republicans pile on frontrunner Trump
Trump leads in polls in many of the states that will vote next week on the so-called Super Tuesday, which could give him the necessary momentum to become the Republican Party's candidate for president.
Al Jazeera's Alan Fisher, reporting from Houston, described the attacks on Trump as "a pretty meaty assault".
"We have seen in the past that Donald Trump has relatively poor debate performances. He's managed to bluster through them through the strength of his personality, but the reality is this race is tightening," Fisher said.
"To win the nomination you've got to get just over 1,200 delegates. Donald Trump has just 79. So the electoral math says he won't win on Super Tuesday, but the reality is if he wins many of these states, including Texas, he's going to be almost an unstoppable force."
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Source: Al Jazeera and agencies