The Democrats lost to Donald Trump and may do it again. How did the world’s oldest political party, which has won four of the past seven presidential elections and received popular-vote pluralities in two more, find itself in this pickle?

One symptom of the party’s ailment is that its four top-polling presidential candidates in national surveys are in their 70s and No. 5 is a 38-year-old former mayor of a city of 102,000. Why haven’t others risen? Where are the candidates with demonstrated appeal to critical segments of the electorate? One answer is that over the past decade the Democrats have had a tough time electing candidates beyond heavily Democratic constituencies.

The decision to enact ObamaCare in 2010 despite its obvious unpopularity—forced through by Speaker Nancy Pelosi over President Obama’s doubts—not only cost Democrats the House but helped prevent the election of Democratic senators and governors in marginal states and produced Republican legislative majorities that dominated redistricting after the 2010 census. It may be reasonable for a party to risk seats to achieve a major policy goal. But the 2010 losses were massive, and current Democratic complaints about health care suggest ObamaCare hasn’t been a policy success.

The Democratic Party has always been a coalition of out-groups. For almost a century after the Civil War it was an awkward alliance of Southern segregationists and Catholic immigrants. Until the 1930s, it had a hard time finding plausible presidential candidates because most of its prominent officeholders were Southerners or Catholics, then considered unelectable nationally. But in 1932 they had a New York governor who was firmly Protestant and a fifth cousin of the popular Republican President Theodore Roosevelt.

Today, with its four top contenders from the heavily Democratic Northeast—Delaware, Vermont, Massachusetts, New York—it has a similar problem. Delaware and Vermont were competitive states when Joe Biden and Bernie Sanders first sought office in the 1970s. But neither man has faced a competitive statewide race in decades.