More than 16 million voters who did not cast a ballot in 2016 have already voted this year, a sign that record-high enthusiasm in November’s elections will lead to an unprecedented turnout across the country. There are indications that the surge is being fueled by younger voters who have been targets of turnout operations funded by Democratic groups, and by minorities who are motivated to vote like never before, data experts keeping tabs on the early numbers say. Already this year, more than 4 million people between the ages of 18 and 29 have cast a ballot after sitting out 2016. They represent about two-thirds of all voters in that age bracket who have voted already. In states where voters can register by party, registered Democrats among those youngest voters outnumber registered Republicans by a nearly three to one margin.