In the final weeks of a tough, expensive re-election campaign for governor of Wisconsin, Scott Walker ran an advertisement that raised eyebrows on both sides of the culture war over abortion.

“Hi, I’m Scott Walker. I’m pro-life,” Walker says in the ad. “But there’s no doubt in my mind the decision of whether or not to end a pregnancy is an agonizing one. That’s why I support legislation to increase safety and to provide more information for a woman considering her options. The bill leaves the final decision to a woman and her doctor. Now, reasonable people can disagree on this issue. Our priority is to protect the health and safety of all Wisconsin citizens.”

The ad aired in October, when polls showed him unpopular with female voters, with his challenger, Democrat Mary Burke, leading among women. This softer tone from a politician with a long record of rolling back access to abortions angered social conservatives, who were upset that Walker appeared to have abandoned his staunchly pro-life views. The shift also outraged reproductive rights activists, who said the ad was misleading to obscure his extreme stances on women’s issues.

In the months since winning re-election, Walker, the son of a Baptist minister, has been under pressure to defend his record on opposing abortion and convince supporters that he is socially conservative enough to be the Republican nominee.

“My policies throughout my career have earned a 100% rating with pro-life groups in Wisconsin,” Walker wrote in an open letter in March. “Just in my first term I signed numerous pieces of pro-life legislation and I will continue working for every life.”

Since being elected governor in 2011, Walker has signed off on legislation requiring women seeking abortions to undergo ultrasounds, prohibiting the procedure from being covered by healthcare plans and defunding Planned Parenthood.

Now, days before he is expected to announce his candidacy for president, the Republican governor may get one more chance to reinforce his conservative credentials should a bill banning abortion after 20 weeks of pregnancy land on his desk.

The Wisconsin bill, which is similar to legislation passed in 14 other states, is rooted in the belief that fetuses can feel pain at 20 weeks, a claim that has been disputed in medical research.

Walker’s office confirmed on Wednesday that he “plans to sign the bill” if it passes the legislature.

But in the runup to his re-election last year, Walker had refused to take a stand on the ban. Pressed in an interview with the Milwaukee Journal Sentinel in mid-October, he demurred.

He said late-term abortions “raised some concerns” and repeated that he believes a fetus is “a human life”. He then offered a hypothetical: what if my wife had been in a terrible car accident while pregnant with one of our sons and lost the baby, he asked rhetorically. “You wouldn’t send just a get-well card you’d probably send a sympathy card to us because we lost that unborn child,” he said.

“To say one thing, when you’re seeking the vote, get elected, then operate in a way that’s completely antithetical to what you said when you were running, is incredibly frustrating,” said Dayna Long, president of the Madison chapter of the National Organization for Women.

“It’s a betrayal and frankly I think it makes him a really untrustworthy politician.”

Some critics say the ban was a calculated move by the governor to attract national conservatives.

Though he has repeatedly pledged his support for the bill, the governor has been more discreet about the genesis of the bill. The New York Times reported that Walker asked legislative leadership to deliver the bill to his desk during a meeting in his office earlier this year. A spokesman with the office of the state senate majority leader confirmed the report.

Wisconsin representative Chris Taylor, the former director of public policy for Planned Parenthood of Wisconsin, who opposes the ban, said she has no doubt the ban is at least in some way a part of a broader political calculation.

“He’ll say anything to get elected,” Taylor said. “And this is a guy who’s done a lot of devastating things for the women of the state.”

Taylor said she is prepared to argue against the bill, which she called “unconscionable”, on Thursday, when the Wisconsin assembly is expected to vote. The state senate approved the bill in June on a party-line vote, with Republicans in favor, after a nearly three-hour debate.

The bill would prohibit abortions 20 weeks after conception. The bill provides some exemptions for women in medical emergencies, but not in cases of rape or incest.

Doctors and medical professionals who perform abortions could face criminal charges, punishable by $10,000 in fines or three and a half years in prison. The legislation also allows the father to sue the doctor for damages.

Supporters of the legislation says it protects women’s health, because late-stage abortions can have more complications, as well as the fetus’s.

“It is undisputed that the risk to women from abortion increases with gestational age,” said Mailee Smith, a staff attorney for Americans United for Life.

“As such, bills limiting abortion at or after 20 weeks protect both women’s lives as well as protect unborn children from the pain inflicted in later-term abortions,” Smith added in a statement.

Abortions after 21 weeks of gestation are infrequent in the United States – nearly 99% of abortions in the US occur before 21 weeks, according to Planned Parenthood. The rate is similar in Wisconsin, where abortion clinics don’t perform the procedure at that point in a pregnancy. (They are performed in hospitals in cases involving medical problems.) In 2013, just over 1% – 89 out of 6,462 – abortions were performed after 20 weeks of gestation, according to state figures.

But opponents of the 20-week bans say that the women who have abortions at this stage in their pregnancy often do so out of medical urgency. Abortions later in the pregnancy, reproductive rights activists say, are more likely to involve severe fetal abnormalities and serious risks to women’s health.

Though the bill carves out exemptions for medical emergencies, women and their doctors have to meet a series of requirements that opponents say are too onerous before the procedure is allowed.

The Wisconsin bill is just the latest in a rash of bills seeking to ban abortion at or earlier than 20 weeks. Such bans challenge the fetal viability standard on abortions established by the 1973 US supreme court decision Roe v Wade, which legalized abortions. Fetal viability is generally believed to occur between 22 and 24 weeks.

Bans in Georgia, Idaho and Arizona have been struck down by courts. The ninth circuit court of appeals struck down the Arizona law in 2013, a decision the US supreme court declined to reconsider. In May, the same court found that Idaho’s law was unconstitutional.

Eleven other states have some version of the 20-week ban in place, according to the Guttmacher Institute, a reproductive rights research group. The US House also recently passed a bill banning abortion at 20 weeks, which includes an exemption for rape. Even if the bill were taken up and passed by the Senate, it would face a veto by President Barack Obama.

“Voters and the public are becoming more attuned to the fact that these are all part of a nationwide scheme to ban abortion altogether,”said Hayley Smith, an advocacy and policy associate at the American Civil Liberties Union.

“They might hear about a 20-week ban this year, and next year they might hear about a bill to close abortion clinics in their state,” she said. “And over time they realize it’s not just one piece of legislation. It’s a whole scheme of legislation designed to ban access altogether.”