Incumbent Mike Bost and Darren Bailey are running in the Republican primary for Illinois’ 12th Congressional District on March 19, 2024.

The district has an R+24 partisan lean in the Cook Partisan Voting Index (PVI), making it the most Republican-leaning district in Illinois. Bost, who has represented the district since 2015, won re-election in 2022 with 75% of the vote.

According to WBEZ’s Alex Degman, “[the] candidates have a lot in common — both are staunchly Christian and hold strong, conservative views on abortion rights, the Second Amendment and immigration. The difference may be in their approach — Bost calls himself a ‘governing conservative,’ which means he stands for conservative values but works with others to pass legislation. … Bailey says Bost’s experience and his collaborative approach are precisely the problem.”

Bost was first elected in 2014 when he defeated incumbent Bill Enyart (D) 53%-42%. Bost served in the Illinois House of Representatives from 1995 to 2015 and was the treasurer of Murphysboro Township. He was an electronic specialist in the U.S. Marine Corps.

Bost has highlighted immigration, abortion, and gun policy as key issues. He has also contrasted his legislative experience and governing approach to Bailey’s. Bost said, “Our real issue [in Congress] is to try to gain ground where we can gain ground and actually govern from the small majority that we have. … Unfortunately, we have people that are more interested in being on social media to get likes and also who work to get on a 24-hour news network.”

Bailey, a farmer, served in the Illinois House and Senate. Bailey was the Republican nominee in the 2022 Illinois gubernatorial election, when he lost 55%-42% to incumbent J.B. Pritzker (D).

Bailey has focused on gun policy. He said he would “die on [his] front porch before [he gave] away [his] Second Amendment rights” and said the Illinois Firearm Owners Identification (FOID) card system was “an infringement that was designed to pilfer money.” Bailey has also criticized Bost’s government experience. “If we want to fix the problems in Washington, we must change the people we send. My opponent has spent 40 years in government and a decade in Washington,” Bailey said.

Former President Donald Trump (R), U.S. House Speaker Mike Johnson (R-La.), and U.S. House Republican Conference Chair Elise Stefanik (R-N.Y.) endorsed Bost. Bailey’s endorsers include Rep. Matt Gaetz (R-Fla.) and Rep. Mary Miller (R-Ill.).