Incumbent Republican Mike Bost faces Democrat Julie Fortier in the Illinois 12th congressional district on November 3, 2026. All major forecasters rate the seat Solid or Safe Republican, consistent with the district’s recent history of 30-plus-point Republican margins in presidential and House voting. Primaries concluded in March with both candidates advancing without significant opposition. Trader consensus on the margin of victory clusters in the 30-40% range for Republicans, reflecting the district’s partisan lean and Bost’s incumbency advantages in fundraising and name recognition. Limited polling and low national attention keep probabilities distributed across those buckets rather than concentrated on one outcome. Late shifts in turnout or a broader midterm wave could narrow or widen the final margin within the resolution window.