It will explain a huge amount about Tuesday's races, and is encapsulated by the latest polling from Alaska:
How can McAdams be so much more popular than Miller yet still be trailing the race? It's because 92% of the small group of voters that does like Miller is planning to vote for him. But only 56% of the voters with a positive opinion of McAdams are intending to cast their ballots for him, while 31% of them are going for Lisa Murkowski.
The results tomorrow will be the results of those who were motivated enough to vote. That's the bleeding obvious, I know. But it presents big problems for a victorious GOP. It will be very hard for them not to be emboldened by their base turnout to do things, or, rather, do nothing, in ways that could come back to haunt them.