The tone reflected the fierce battle underway ahead of “Super Tuesday” next week.

Rivals Ted Cruz and Marco Rubio mounted a furious assault against Donald Trump in Thursday’s Republican presidential primary debate, blasting the frontrunner for hiring foreigners and challenging his commitment to conservative principles.

Knowing that they need to change the campaign trail narrative quickly or risk Trump coasting to the Republican nomination, the two freshman U.S. senators launched broadsides against the brash billionaire, who lashed out at his challengers in what quickly devolved into a shouting match.

Rubio, seen by many as the primary mainstream challenger to Trump, immediately berated Trump over his immigration positions, knocking him for having supported a pathway to citizenship before turning sharply conservative on the controversial issue.

He took the billionaire to task for having “hired a significant number of people from other countries to take jobs that Americans could have filled” in Trump development projects.

He pointed to articles that described a 1980s lawsuit by a workers union against Trump for hiring 200 illegal immigrants from Poland to build Trump Tower in New York.

Rubio also accused Trump of starting a “fake university” that bilked students out of thousands of dollars, and that if the real estate icon didn’t receive a massive inheritance from his wealthy father he would be “selling watches in Manhattan.”

Trump bristled, and pushed back fiercely.

“I’ve hired tens of thousands of people,” said in his rejoinder to Rubio. “You haven’t hired one person, you liar.”

The tone reflected the fierce battle underway ahead of “Super Tuesday” next week, when 11 states including Cruz’s huge home state of Texas go to the polls in perhaps the most consequential voting day of the 2016 primary campaign.

Should Trump run the table or win most of the states, it may well be lights out for his rivals, who also include two lesser candidates in retired neurosurgeon Ben Carson and Ohio Governor John Kasich.

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