The Republican presidential contenders are scrambling before Saturday's primary election to convince South Carolina voters they're each the toughest on abortion.

It's crucial for any Republican to have a strong stance against the controversial procedure in South Carolina, a conservative state poised to pass the latest so-called "fetal pain" law banning mid- and late-term abortions.

Front-runner Donald Trump has more work to do than any of his five opponents, as he has previously supported partial-birth abortion and used to describe himself as "pro-choice."

He's been trying hard this week to convince voters he has had a change of heart, saying he would sign a bill defunding Planned Parenthood in an interview with the Christian Broadcasting Network's David Brody that aired Thursday.

"As long as they're involved with abortion, as far as I'm concerned forget it, I wouldn't fund them," Trump said.

Trump's efforts haven't won over most of the prominent anti-abortion leaders. Susan B. Anthony List, a group focused on electing anti-abortion women to office, is urging voters to support any Republican candidate except for the billionaire businessman.

SBA List spokeswoman Mallory Quigley said Thursday she doesn't dispute Trump's "conversion" against abortion, but said he's still not the leader who abortion foes want to see in the White House.

"It's not enough to just check the box," Quigley said. "We need a leader who goes on offense, who is willing to expose the abortion extremism of the Democrats, who lays out clear pro-life policy goals and pledges to surround themselves with pro-life champions."

South Carolina is among the Republican-led states that have passed new abortion regulations over the last few years. Last year, the state's House and Senate passed a ban on abortions past 20 weeks of pregnancy, and this year the versions are being combined in a conference committee.

"We do anticipate we will have a final bill and Gov. Haley will sign it," said Holly Gatling, director of South Carolina Citizens for Life.

Gov. Nikki Haley signed a 2012 law that requires doctors to care for infants who are born alive after a botched abortion. The state also has passed laws requiring abortion facilities to comply with the standards of ambulatory surgical centers and get hospital privileges for doctors.

"South Carolina was the first state to pass a clinic regulation," Gatling said. "Our clinic regulations set the standard."

Sen. Ted Cruz has has been at Trump's throat all week, trying to catch him in the polls by highlighting his record on abortion. Cruz ran an ad that prompted a cease-and-desist letter from the Trump campaign demanding Cruz stop running it. Cruz is also going after Sen. Marco Rubio, who is trying to nab second place.

Cruz and Rubio are virtually identical in their positions on the issue, both opposing abortions in cases of rape and incest and both voting for bills that defunded Planned Parenthood. Rubio has been even more vocal on the topic than Cruz in the GOP debates, stating several times that he supports abortion only if the woman's life is at stake.

Yet last week, Cruz told an evangelical audience that Rubio voted for a spending bill that included funding for Planned Parenthood, trying to suggest his Florida colleague was weak on the issue.

For years, bipartisan federal spending bills have allowed reimbursements to Planned Parenthood and other health providers for services for low-income patients, as long as those funds aren't used for elective abortions. Rubio has voted for some of those bills, as have many other Republicans opposed to abortion.

Cruz's tactic against Rubio earned him some indignation from abortion opponents including National Right to Life President Carol Tobias and former Sen. Rick Santorum, who said Cruz's attack was a "disservice to the pro-life cause."

Besides attacking his opponents, Cruz also has announced a "Pro-Life Coalition" of activists backing him in South Carolina.

"Sadly, too many Republicans have gone wobbly when it comes to one of the most important planks in our party's platform," Cruz said in a video he released Wednesday. "Even now, there's a candidate in the race playing games with the sanctity of life … Donald Trump spent most of his adult life prior to this election enthusiastically pro-abortion."

Meanwhile, Gov. John Kasich is about to sign to a new Ohio law stripping an estimated $1.3 million from Planned Parenthood clinics in his state.

Kasich spokesman Joe Andrews said Thursday that the governor's office had just received the bill from legislative leaders and intends to sign it as soon as possible, although it's unlikely he will have time to do so before Saturday's primary.

"It will be signed at our earliest possible time," Andrews said.