After 31 primaries had been completed by July, a Pew study found that Democratic participation came close to doubling that of 2014, rising from 7.4 million to 13.6 million. Republican turnout grew but more modestly, from 8.6 million to 10.7 million. Kyle Kondik, an analyst at UVA’s Center for Politics, cautioned that while primary turnout is not necessarily predictive of general election turnout, the trend is clear when taken with other data, like fundraising, polling and even hiring on K Street, the Washington home to many lobby firms, which are rapidly recruiting Democrats in anticipation of...