"If Republicans don't ever have that big advantage that they had in 2014, it's going to be interesting to watch and see if there is still a late rush of Democratic ballots in those last few days," said Ryan Winger with the polling firm Magellan Strategies.
Unaffiliated voters, who make up the largest sector of registered voters, have turned in ballots well ahead of their 2014 pace. So far, close to a quarter-million have returned their ballots. Of those unaffiliated voters, around half also chose to participate in the primary, something they could do for the first time in 2018.
"Just that in and of itself, opening up the political process to them, might have got them more engaged in politics," Winger said. "Maybe that also carries over to them returning their ballots a little bit earlier than they did in 2014."