The Republican primary just reached new levels of nastiness ahead of the big debate

The Republican presidential race has reached new levels of infighting ahead of the Tuesday night debate hosted by the Fox Business Network.

Real-estate mogul Donald Trump, naturally, led the way with the most personal insults.

At a Monday night rally in Springfield, Illinois, Trump attacked both Sen. Marco Rubio (R-Florida) and retired neurosurgeon Ben Carson, two of his leading opponents in the polls. 

Trump blasted both for being "very, very weak" on illegal 

immigration. He also hit Rubio for his poor Senate-attendance record and for drinking too much waterduring his 2013 response to the president's State of the Union address.

"I don't care if he's a nice guy. Remember when he was doing the message to the president? Remember the thing with the water? This guy gets the greatest press. So he's sweating and sweating, pouring sweat," Trump recalled. "I notice. I say,, 'Man is he sweating!'" 

And some of the top-tier candidates who have thus far 

largely declined to blast their rivals are increasingly taking their gloves off, as well.

Rubio hit back quickly after The New York Times reported Monday night that former Florida Gov. Jeb Bush's (R) big-money super PAC was testing anti-Rubio messaging and boasting that it could spend as much as $20 million to take Rubio down a notch.

The senator's operation responded by releasing a video reminding viewers that Bush once vowed to run a "joyful" campaign and that Bush once used to shower praise on Rubio as a potential vice-presidential pick in 2012.

Bush and Rubio, a former Florida house speaker, were allies in the Tallahassee statehouse. Some Bush supporters have even reportedly taken to calling Rubio "Judas" because of his lack of deference to Bush in the race. 

Source: Business insider