OSHKOSH, Wis. — Republican Wisconsin Gov. Scott Walker, one week after launching his bid for the 2016 presidential nomination, signed a bill Monday that outlaws non-emergency abortions at or beyond 20 weeks of pregnancy.

Abortion is a core issue for the conservative Republican base whose support Walker will seek, as he tries to stand out in a crowded presidential field that includes former Florida Gov. Jeb Bush, Florida Sen. Marco Rubio and billionaire Donald Trump.

While Walker has a long history of opposing abortions, it’s an issue where he could be targeted by rivals: Just nine months ago, he ran a television ad during his gubernatorial re-election campaign where he said whether to obtain an abortion is an agonizing decision between a woman and her doctor.

Walker’s record includes defunding Planned Parenthood; requiring abortion doctors to have admitting privileges at nearby hospitals, a law currently blocked by a federal court judge; and requiring women to have ultrasounds and be shown images of the fetus before having an abortion.

During his re-election campaign last year, Walker refused to say whether he would support a 20-week abortion ban.

But in the face of questions from anti-abortion conservatives over his commitment to the issue in light of the campaign ad, Walker in March came out in support of the 20-week abortion ban.

“The truth is that Scott Walker lied to Wisconsin voters when he was elected governor after saying that abortion is between a woman and her doctor,” said Sasha Bruce with NARAL Pro-Choice America, a leading abortion rights advocacy group. “Now, in an effort to win the votes of the extreme base of the Republican Party, Walker has traded the health and well-being of women and families to score cheap political points.”

The governor’s signature makes Wisconsin the 15th state to pass similar bans. There is no exception for pregnancies resulting from rape or incest.

The new law – which cleared the Legislature without any Democratic support – is expected to be challenged in court. Walker, speaking with reporters after the bill signing, said he was confident it would survive any legal challenge, calling the five-month ban a “reasonable standard.”