Former Sen. Rick Santorum (R-Pa.) is questioning Sen. Ted CruzRafael (Ted) Edward CruzOvernight Finance: GOP criticism of tax bill grows, but few no votes | Highlights from day two of markup | House votes to overturn joint-employer rule | Senate panel approves North Korean banking sanctions GOP criticism of tax bill grows, but few ready to vote against it Anti-gay marriage county clerk Kim Davis to seek reelection in Kentucky MORE's (R-Texas) social conservative credentials, saying he has a "libertarian streak" on many key issues.

“[Cruz has] sort of a libertarian streak that used to very much be a disqualifier among conservative circles,” Santorum said on Fox News’s “America’s Newsroom" on Tuesday.

Santorum said that many issues important to social conservatives must be dealt with at the federal level and not left up to the states.

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“Take the issue of marriage,” Santorum continued. "Sen. Cruz, [Sen.] Rand Paul [R-Ky.] and frankly others have said, ‘We’re going to let the states decide these issues. We’re not going to do anything at the federal level.’"

“That means if the states want to adopt same-sex marriage, fine, polygamy, I guess that’s fine, or really any type of marriage,” the 2016 GOP presidential candidate added.

“I don’t take that opinion, and most conservatives say there is a law, a higher law, that people are accountable to. [It is] a natural law, the law of what is right and things that are moral and just.”

Santorum accused Cruz of being too deferential to the Supreme Court.

“Ted Cruz is a very successful trial lawyer,” he said. "He gives a lot of credence to the courts."

“I think a lot of conservatives are very frustrated with the judicial activism we see at the court and are looking to stand up to the court when it violates the Constitution,” Santorum continued.

“[They want someone] who will stand up to the court and say, ‘No, you can’t do that.' That’s another difference between where I think most conservatives are and the approach he has taken on some of these issues.”

Santorum's comments come as he looks to gain traction with social conservatives in Iowa ahead of that state's first-in-the-nation caucuses on Feb. 1. Santorum is hoping to repeat his stunning come-from-behind victory in the Hawkeye State’s 2012 caucuses.

Cruz currently leads the pack in the state with 30 percent support, according to the latest RealClearPolitics average of polls, with Santorum trailing at under 1 percent.