The Illinois 15th congressional district’s R+20 Partisan Voter Index and incumbent Republican Mary Miller’s strong primary performance have anchored trader expectations for a substantial Republican margin against Democrat Jennifer Todd in the November 3 general election. With primaries concluded in March and all major forecasters rating the seat Solid or Safe Republican, the absence of late-breaking polling shifts or national headwinds has kept probability concentrated in the 25-35 point Republican victory bands. Fundraising gaps favoring Miller further reinforce baseline turnout patterns typical of this downstate rural and suburban district. The tight spread among adjacent margin buckets reflects uncertainty over the precise degree of compression a contested race may produce relative to prior unopposed or higher-margin cycles, while the low probability on a Democratic win or sub-20 point outcome underscores structural barriers absent major unforeseen developments before Election Day.