Former Sen. Rick Santorum called rival Rep. Ron Paul disgusting during last-minute stumping for the Iowa caucuses Tuesday, signaling a nasty turn inr the Republican presidential race.

Santorum, a former U.S. senator from Pennsylvania, told an Iowa crowd he blamed Paul for automated robocalls that claimed he was pro-abortion and against the Second Amendment, The Huffington Post reported, both stances the social conservative says he is against.

Tuesday morning on Fox and Friends, Santorum said Ron Paul is disgusting for being behind the calls.

Paul's son, Sen. Rand Paul of Kentucky, has been campaigning with his father in Iowa all week but told Fox News he hadn't heard the automated message.

I haven't heard the robocalls, but the thing is, he (Santorum) hasn't been scrutinized yet, so it's his turn, Rand Paul told the network.

While the GOP candidates have sniped at each other in debates the past few months, most have saved their most bitter attacks for President Barack Obama. But candidates are starting to take off the gloves when addressing each other, and Santorum isn't the only one.

Newt Gingrich called Mitt Romney a liar on CBS News Tuesday morning, a couple of days after he said he was Romney-boated by what he said are $3.5 million attack ads by political groups supporting the former Massachusetts governor.

He's not telling the American people the truth. It's just like his pretense that he's a conservative, Gingrich said. Here's a Massachusetts moderate who has tax-paid abortions in 'Romneycare,' puts Planned Parenthood in 'Romneycare,' raises hundreds of millions of dollars of taxes on businesses, appoints liberal judges to appease Democrats, and wants the rest of us to believe somehow he's magically a conservative.

Romney, however, shied away from directly attacking the former House speaker Tuesday morning on Fox and Friends.

Well, I understand Newt must be very angry and I don't exactly understand why, but look, I wish him well, Romney said. It's a long road ahead. He's a good guy. I like him and [wife] Callista. We've got many months ahead of us, so I'll leave it at that.