Presidential candidate Rick Santorum says that Republicans can't win if they nominate a "Tweedledum" like former Massachusetts Gov. Mitt Romney.


In an Monday interview on CBS, Santorum told host Charlie Rose that if he could stay in the race until the convention, delegates would want to nominate a true conservative instead of "the establishment, moderate candidate from Massachusetts."

"We have proven in the past when we nominate moderates, when we nominate Tweedledum versus Tweedledee, we don't win elections. We win elections when there are clear contrasts and bold choices and that is what we are going to do in this election," the candidate asserted.

"It really has to do with what your principles and your core is," he continued. "I have a core. I'm someone who has really strong convictions about the limited role of government, about the importance of having a strong defense, you know, lowering taxes and getting regulation down. And that's a sharp contrast with Mitt Romney, who is for Romneycare, the blueprint for Obamacare -- advocated for Romneycare, advocated for government mandates at the federal level."

"This is someone who doesn't have a core. He's been on both sides of every single issue in the past ten years."

Over the weekend, Romney easily won all the delegates in Puerto Rico with 83 percent of the vote.

Santorum, however, was already looking forward to the Illinois primary as the key to his nomination.

"This is a primary, and turnout is everything," the former Pennsylvania senator said. "You do your job, you do your job, then this is the pledge... If we're able to come out of Illinois with a huge or surprise win, I guarantee you, I guarantee you that we will win this nomination."

A Public Policy Polling survey released on Monday showed Romney with a 15 point lead over Santorum in Illinois.

Watch this video from CBS's This Morning, uploaded March 19, 2012.

(H/T: CBS News)