Debating whether Rick Santorum or Ron Paul is more pro-life is kind of like debating whether Iowa or New Hampshire is colder this time of year.

With a few degrees difference between them on any given day, both states are frigid and both candidates decidedly are against abortion.

But the shade that separates them suddenly is a campaign trail topic as Santorum accuses Paul's campaign of being behind Iowa robo-calls suggesting the strident social conservative is pro-choice.

"Ron Paul is disgusting," Santorum remarked to Fox News reporters Tuesday, in reference to the calls.

Paul's campaign recently has tried to paint Santorum as a "liberal" on some issues, and the alleged addition of abortion to that list struck a nerve with the former Pennsylvania senator, who was in office from 1995-2007.

Asked about Santorum's outburst, Paul told Fox News "that's not very nice," and that Santorum is trying to "deflect away from some of the charges made against him." Paul noted that Santorum had supported his fellow Pennsylvania former senator, Republican-turned-Democrat Arlen Specter, who is pro-choice.

Paul's son Kentucky Sen. Rand Paul -- without taking responsibility for the calls -- claimed on Fox News that Santorum backed funding for Planned Parenthood. He then went on to criticize Santorum for backing foreign aid and increased federal education funding.

Paul did not elaborate, but was likely referencing Santorum's votes for federal budgets which included Title X family planning funding -- some of which goes to Planned Parenthood. That funding is not supposed to go toward abortions, and House Republicans since winning the majority last year have tried to cut off the funding to Planned Parenthood altogether out of an abundance of caution.

"He hasn't been scrutinized yet, so it's his turn," Paul told Fox Business Network.

Still, Paul and his surrogates haven't said much else about Santorum's abortion record, likely because he is about as far right on the issue as a GOP candidate can get.

He authored the 2003 federal partial-birth abortion ban. He supported another federal law to give legal rights to infants born alive after failed abortions, and one that acknowledged unborn children as victims if they are hurt or killed in a violent crime.

"Rick Santorum not only believes but cherishes the ideal of a culture of life," his campaign website states. A recent campaign ad touted his effort to end partial birth abortions.

On the taxpayer funding of abortion question, the conservative Family Research Council lists every GOP candidate as opposed.

And Santorum, along with Paul, signed the Personhood USA pledge which declares opposition to abortion in all cases except when the life of the mother is in danger. Even in that instance, the pledge says "every effort should be made to save the baby's life as well; leaving the death of an innocent child as an unintended tragedy rather than an intentional killing."

Santorum, perhaps putting a fine point on where he stands, has campaigned in the final hours before the Iowa caucuses with the Duggar family, stars of TLC's "19 Kids and Counting."

Paul as well has touted his anti-abortion credentials in campaign ads. His campaign literature cites his record as a "pro-life OB/GYN who has delivered over 4,000 babies."

In explaining the origin of his views, Paul cites his experience in medical school having to watch an abortion being performed and says he never found the procedure necessary to save the life of a mother.

Paul advocates for the effective nullification of Roe v. Wade and the passage of a new federal law that defines life as beginning at conception. He also opposes funding to Planned Parenthood.

Some pro-life groups, though, have raised concerns that Paul's states'-rights views occasionally trump the call for stricter anti-abortion enforcement on the federal level. He voted, for instance, against the Unborn Victims of Violence Act, which Santorum supported.

In signing the Personhood USA pledge, which calls for Fourteenth Amendment protections for the unborn, he included a statement saying the Fourteenth Amendment -- which says nobody should be deprived of life without due process -- should not "cancel out the Tenth Amendment," which pertains to states' rights.

Paul warned in that statement about a "federal police force" on the issue, or the possibility of a "Federal Department of Abortion."

Asked to clarify the position, Paul told the group he believes the federal government should "define life" as beginning at conception, and then leave it up to the states to determine enforcement.

Personhood USA later said it had "serious concerns" about Paul's "inconsistencies" on the issue.

Personhood USA President Keith Mason told Fox News on Tuesday that Paul's stance is "a little bizarre."

"It seems that he at some level values the reducing of the federal government higher than human life," he said.

But in the eyes of abortion-rights supporters, both Paul and Santorum are quite pro-life.

According to NARAL Pro-Choice America, Santorum in the Senate voted "anti-choice" 72 times, "out of 73 opportunities." The group called him "extreme."

The same organization said Paul voted "anti-choice" 93 times in the House, out of 106 opportunities.

Rand Paul, interviewed on CBS News on Tuesday, conceded Santorum is "very conservative" on social issues, without discussing abortion.

But he repeated his father's earlier criticism of Santorum's record on other issues.

"On economic issues, like foreign aid, he's voted for foreign aid repeatedly. He voted to double the size of the Department of Education. Old school Reagan Republicans don't believe in the Department of Education," he said.

On Fox News, Santorum questioned how the Paul family could claim he's liberal considering the rap on Santorum's campaign is that he's "too conservative to win."

"Coming from someone who's in the Dennis Kucinich wing of the Democratic Party on national security, being called a liberal by him is a little bit, you know, just almost ridiculous," Santorum said. "I have credibility across the board on all the issues of standing for the conservative principles that made this country great."