As always, the most important thing to look out for is vote share, not margins. Kelly has a ceiling of 47% here and is often below that.
That 50% rule is bunk. Susan Collins, Thom Tillis, and Joni Ernst consistently polled in the low forties before winning re-election.
Not the point. Polls should be monitored to assess whether or not candidates are growing their vote share, and how critical the undecided vote and potential turnout gaps could be in deciding the final result. The candidate with the more inflexible base (typically the democrat in states with significant, population-dense POC regions) tends to be the one who hits their ceiling first, and this should be something Kelly's campaign is paying close attention to. Undecideds tend to break in favor of the state's partisan lean (e.g. Hawley consolidating undecideds in Missouri in 2018), another red flag for Kelly in a state where trends are in his favor but the national environment probably won't be.
