A trigger law is a nickname for a law that is unenforceable, but may achieve enforceability if a key change in circumstances occurs.
In the United States, twelve states — Arkansas, Idaho, Kentucky, Louisiana, Mississippi, Missouri, North Dakota, Oklahoma , South Dakota, Tennessee, Texas,  and Utah have trigger laws that would automatically ban abortion in the first and second trimesters if the landmark case Roe v. Wade were overturned.    Illinois formerly had a trigger law (enacted in 1975), but repealed it in 2017.    Also, nine states — Alabama, Arizona, Michigan, West Virginia, and Wisconsin as well as the already mentioned Arkansas, Mississippi, Oklahoma, and Texas, still have their unenforced pre-Roe abortion bans on the law books. Those laws are not currently enforceable due to Roe, but could be enforced if Roe were overturned. 
The Affordable Care Act allowed states to opt in to a program of health care expansion, which allowed more residents to qualify for Medicaid. The cost of this expansion was primarily borne by the federal government, but the percent paid by the federal government was scheduled to decrease each year, reaching 95% by 2017 and below 90% by 2021; the remainder would be assumed by the state. As of 2017, eight states had laws that would trigger an end to participation in Medicaid expansion, if federal funding fell below a particular level.   [ needs update] Unlike the abortion trigger laws, these are not unconstitutional at the moment and are only inactive because they rely on certain conditions to activate.
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- Smith, Kate (April 22, 2019). "Abortion would automatically be illegal in these states if Roe v. Wade is overturned". CBS News.
- Sarah Mansur, Bill removes trigger from abortion law, but impact unclear, Chicago Daily Law Bulletin (May 1, 2017).
- John Dempsey, Rauner signing of abortion bill angers conservatives, WLS-AM (September 29, 2017).
- Note, Recent Legislation: Illinois Repeals Anti-Abortion Trigger Law, 131 Harv. L. Rev. 1836 (2018).
- Schencker, Lisa. "Medicaid expansion could end early in Illinois under Senate Obamacare replacement bill". chicagotribune.com. Retrieved 2021-09-03.
- says, Mike. "NM Group Slams Obamacare Replacement Bill Ahead of Senate Debate - El Paso Herald Post". Retrieved 2021-09-03.
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