The nation has reached the halfway mark in the 2016 presidential primaries. It’s difficult to draw big conclusions from the small slice of Americans who vote in primaries, but turnout among Democratic voters has been less enthusiastic than among Republicans, with roughly five million more votes cast in Republican primaries than in Democratic ones. That suggests Democrats will need to do more to motivate their constituencies to vote in November.

The good news for the country is that 2016 primary turnout is high over all. In November, “levels of engagement could be at the high end of the range that we’ve seen in the last century of American politics, and it’s possible they could go higher,” said Michael McDonald, who runs the University of Florida’s United States Elections Project.

Young people have been unusually engaged this year, and not only on the Democratic side. They have set all-time turnout records in nearly every Republican primary, according to the Center for Information and Research on Civic Learning and Engagement at Tufts University.

The group’s analysis showed that Donald Trump drew more young voters than his Republican rivals, but his lead was far from decisive. He has received slightly fewer votes from young people than Hillary Clinton. Bernie Sanders, the overwhelming favorite of millennials, has received more votes from the young than Mr. Trump and Mrs. Clinton combined.