Mr. Rubio, the favourite of the party establishment and Mr. Cruz, who is ideologically a Christian revivalist and an insurgent like Mr. Trump, have been at each other’s throat through the season in an effort to establish their own individual credentials.

Mr. Trump’s march had continued unchallenged meanwhile and he leads in 10 of the 11 States in latest polls.

In a last ditch effort to stop him in his tracks, Mr. Rubio and Mr. Cruz pounced on Mr. Trump from both sides during the last presidential debate before Super Tuesday. As the Senators cornered him for his refusal to release his tax details; for hiring foreign workers in his companies — allegedly illegally; his relatively liberal old views on abortion and gay rights and his contributions to the Clinton Foundation, the man whom Jeb Bush had once accused of trying to “insult his way to the presidency,” appeared to be at the receiving end, for once.

Mr. Trump squirmed, searched for words and repeated himself many times. Mr. Cruz said after the debate that Mr. Trump could not offer “substance or details” of any of his plans, not a great disadvantage with the Republican voters, going by the trends so far. The audience at the debate, however, cheered the senators when they went after Mr. Trump and commentators appeared unanimous and gleeful that he was confronted.

At one moment that typified the savage wit that characterised Mr. Rubio’s assault style, he questioned Mr. Trump’s claims to be a successful businessman. “If you hadn’t inherited $200 million from your father, you'd be selling watches on the streets of Manhattan.” Mr. Trump tried hard to defend his reputation as a successful businessman, because his entire campaign is built on that claim, but huge applauds for Mr Rubio from the audience drowned his voice. Mr. Trump corrected Mr. Rubio saying that he had borrowed one million from his father but those details did not matter. “If he builds the wall the way he built Trump Towers, he'll be using illegal immigrant labour to do it,” Mr. Rubio told Mr. Trump.

After the debate Mr. Cruz complemented Mr. Rubio for taking on Mr. Trump. Both had in the initial days tried to keep Mr. Trump in good humour in the hope that he would drop out soon. Mr. Trump’s agony on the debate stage could have enthused Republican donors and establishment, but that may not necessarily pull the plug on his campaign.