I ask myself how this issue applies to Virginia. Say in early 2021 Governor Ralph Northam resigns to take a cabinet post under a Democratic president, would then-succeeded Governor Justin Fairfax be able to run for reelection later that year? In history, there is no precedent.
Yes, because he wouldn't be running for reelection, he'd be running for election, unless he chose to run for his old office again since Virginia has no term limits on being Lieutenant Governor. Indeed, given how late in the election cycle this would likely happen, it's probable that Fairfax would run in 2021 for whatever office he'd been planning on running anyway, which very well could have been governor.
Bump. This may soon be tested.