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In last year’s midterm elections, Democrats won 31 congressional districts that President Trump had carried in 2016 — including in the suburbs of Atlanta, Chicago, Des Moines, Detroit, Oklahoma City, Phoenix, Pittsburgh and Richmond, Va., as well as in more rural parts of Maine, Minnesota, New Mexico and Wisconsin.

How did the Democrats do it? By running a smart, populist campaign that focused above all on pocketbook issues like affordable health care and good jobs. The Democrats who won in these swing districts didn’t talk much about Trump, the Russia scandals, immigration or progressive dreams like single-payer health care. They focused on issues that affect most voters’ daily lives.

Theda Skocpol — the Harvard social scientist who has studied the Tea Party and the anti-Trump resistance, among many other things — has a new op-ed in USA Today that argues that the 2020 Democratic presidential candidates are ignoring the lesson of 2018. By doing so, Skocpol says, they are increasing the chances that Trump will win re-election. As Democrats prepare for their second round of debates this week, I think Skocpol’s message is worth hearing.