Late cross‑party endorsements rarely flip Senate

A high‑profile endorsement of an opposing‑party Senate candidate in the final days can create headlines and narrative momentum, but in most modeled cases it produces only small shifts because voters have largely decided and undecided pools are small. The real effects are often indirect — altering news cycles, donor flows, and localized turnout — and depend on seat‑specific polls, undecided shares, and campaign reactions. — Frames how analysts, campaigns, and media should treat eleventh‑hour endorsements: as potential narrative accelerants rather than presumptive game‑changers unless the race is extraordinarily tight and undecided shares are large.