Someone finally got through to Marco Rubio and Ted Cruz: The imperative in the GOP primary is bringing down Donald Trump.

Very early on, Rubio showed his aggressiveness by challenging Trump on a topic he has dominated through the primary: immigration. In his answer to a question about immigration reform, Rubio accused Trump of hiring "a significant number of people from other countries to take jobs that Americans could have filled." How did Trump respond? He more or less confirmed it:

"Everybody agrees with me on that. They were part-time jobs. You needed them, or we just might as well close the doors, because you couldn't get help in those hot, hot sections of Florida."

Rubio then hit Trump for having to pay a $1 million fine for hiring illegally present Polish construction workers for his hotels: "Look it up," he told viewers. Later, the two had this exchange:

RUBIO: "You lied about the Polish workers."

TRUMP: "Yes, yes, yes. 38 years ago."

RUBIO: "Oh, he lied 38 years ago. All right, I guess there's a statute of limitation on lies."

Rubio also went after Trump for his lack of specifics on, well, pretty much everything. Specifically on health care, Rubio argued Trump had offered nothing more than allowing insurers to compete across state lines. There were a couple of revealing exchanges. First, between the two candidates:

RUBIO: "All right. So, that's the only part of the plan? Just the lines?"

TRUMP: "The nice part of the plan -- you'll have many different plans. You'll have competition, you'll have so many different plans."

RUBIO: "Now he's repeating himself."

TRUMP: "No, no, no. (inaudible) I watched him repeat himself five times four weeks ago..."

RUBIO: "I just watched you repeat yourself five times five seconds ago."

TRUMP: "I watched him meltdown on the stage like that, I've never seen it in anybody..."

RUBIO: "I see him repeat himself every night, he says five things: Everyone's dumb; he's gonna make America great again; we're going to win, win win; he's winning in the polls; and the lines around the state. Every night."

Then moments later came this between Trump and moderator Dana Bash:

BASH: "Is there anything else you would like to add to that?"

TRUMP: "No, there's nothing to add. What is there to add?"

Oh, I don't know: Maybe everything?

When Rubio wasn't hitting Trump on his lack of specifics, Cruz was hammering his lack of conservative credentials. He questioned Trump's trustworthiness when it comes to choosing solid judicial nominees. He pointed out Trump's many past donations to Democratic candidates, including John Kerry in 2004. He reiterated that Trump supports Planned Parenthood (which Trump confirmed). He called out Trump for being a past advocate of socialized medicine.

While the Trump campaign in general and much of Thursday night's debate specifically have been reminiscent of a WWE match, the Rubio-Cruz effort didn't only remind me of a tag team. Maybe it's because the March 1 primaries, including Georgia's, have been branded the "SEC primary," but I was also put in the mind of the old BCS system. I'm talking about rooting for one of your rivals to beat another because it ultimately helps your own. That seemed to be the guiding principle for both Cruz and Rubio during the debate.