The Senate is set to take a procedural vote on a House-passed bill that would ban abortion after 20 weeks of pregnancy, part of a long-running strategy to set up a legal challenge to Roe v. Wade.

In a 2015 article for Mother Jones, Molly Redden delved into the history of state 20-week bans, which were designed from the start to “push the envelope” on Roe:

In 1984, these bills became a formal strategy for defeating Roe. That’s when a Northwestern University law professor named Victor Rosenblum proposed that abortion opponents should seek to pass laws that gnawed at its edges, and hope that judges would let those revisions stand. The so-called incrementalists notched their biggest victory in 1989, when the Supreme Court upheld parts of a controversial Missouri law that required doctors to perform costly viability tests before performing abortions for women who appeared to be at least 20 weeks pregnant. The case, Webster v. Reproductive Health Services, demonstrated just how powerful a weapon a 20-week measure could be. Justice Thurgood Marshall’s papers revealed that the conservative majority in Webster had come within one vote of using the 20-week provision to strike down Roe entirely. The liberal justices went as far as drafting a dissent that read, “Roe no longer survives.” Samuel Lee, who wrote that provision of the Missouri bill while he was a lobbyist for Missouri Citizens for Life, says the 20-week requirement “was designed as an opportunity to attack [Roe]” and the viability framework it established. “The 20-week gestational age was chosen to push the envelope on when the state’s interest in protecting the life of the unborn could take place,” he explains. “It was chosen because it was earlier than the earliest limits of viability at the time, but not so early that the unborn child could never be viable.”

Speaking at an event connected to last week’s March for Life, an attorney with the Religious Right legal group Alliance Defending Freedom said that since 20-week bans have not yet sparked the big court case that the anti-choice movement has been hoping for, ADF is now working to introduce strategically placed 15-week bans in certain states in order to “bait” the pro-choice movement into a lawsuit that they hope will lead to a reconsideration of Roe. What she said was the first one of these was introduced last week in Mississippi.