If Granholm really wanted to be a Senator, she'd probably have run earlier. Even if you limit it to open seats, she passed up opportunities in 2014 (when her governorship was fresher in peoples' minds, though not always positively) and 2024.

By 2026 it'll have been 20 years since she was last on a ballot, though of course she's done a lot of worthy stuff since leaving office. Fortunately our MI bench is big enough that we aren't reliant on a few stars or past officeholders to win.