What do you do well that the other party does not do?

Democrats are running away from that question and paying for it.

You can already some see of that impatience in this year’s elections. As my colleague Nate Cohn has explained, the Democrats’ voter-turnout efforts appear to have succeeded in several battleground states, according to early evidence. Democrats didn’t lose Senate seats in Colorado and North Carolina because turnout was lower than in a normal midterm. They lost, in significant part, because they failed to persuade swing voters — in spite of the unpopularity of the Republican Party and its positions.

Why might that be? The economy is the obvious culprit. Weak income growth has helped make Mr. Obama unpopular and made most Americans unhappy with the country’s direction. No wonder people voted against his party, just as they voted against the party in power at previous times when incomes were stagnant.

Slow-growing incomes won’t necessarily keep Hillary Clinton — or whoever is the Democrat nominee — from becoming president in 2016. But if she can’t persuade Americans that she has a plan for dealing with the great wage slowdown, it will be her biggest vulnerability.

Also one surefire way to fail at persuading voters you care about stagnating wages would be to nominate Hillary.