I have seen that in the 2018 midterms, the turnout rose from the elections in 2014. Though the increase was across the board, some governor's races had higher increases than the national increase from 2014 of about 30 percent for Congress. In Minnesota and California (and California in particular), turnout surged on both sides, and especially for the Democratic candidate.
The most stunning statistic to me is the governor's opponent in California (John Cox) got more votes than Donald Trump did and he still lost by a greater margin than the previous Republican candidate. In Minnesota, the governor got 1.39 million, slightly more than Hillary Clinton but fewer than Obama. The previous one got 0.99 million. What caused this turnout surge in those two states? I believe it is related to the fact that both states haven't had three consecutive Democratic gubernatorial terms. I also think it was a mass preemptive measure to keep the governorship under Democratic control. Is that possible? Just wondering.