The pattern emerges whenever a Republican-led state imposes new restrictions on abortion: People seeking the procedure cross state lines to find treatment in places with less-restrictive laws.

Now, a prominent antiabortion lawmaker in Missouri, from where thousands of residents have traveled to next-door Illinois to receive abortions since Missouri passed one of the country’s strictest abortion laws in 2019, believes she has found a solution.

An unusual new provision, introduced by state Rep. Mary Elizabeth Coleman (R), would allow private citizens to sue anyone who helps a Missouri resident obtain an abortion out of state, using the novel legal strategy behind the restrictive law in Texas that since September has banned abortions in that state after six weeks of pregnancy.

Coleman has attached the measure as an amendment to several abortion-related bills that have made it through committee and are waiting to be heard on the floor of the House of Representatives.

Abortion rights advocates say the measure is unconstitutional because it would effectively allow states to […]