Pew's numbers look eerily similar to the results of the 1920 election, the biggest repudiation of a president's party ever. Woodrow Wilson was president then, and his party's nominee, James M. Cox, won only 34 percent of the vote. Republican Warren G. Harding won 60 percent and carried every non-Southern state.
Wilson and Obama have some things in common. Both were happy to live in university communities. Both had minimal experience in high political office. Both got heavily Democratic Congresses to pass major legislation in their first terms. Both were cheered by crowds of thousands in Europe.
Wilson led the nation to victory in World War I, but his last two years were disastrous. He suffered a disabling stroke. His Versailles Treaty was rejected by the Senate. The nation was hit by inflation and recession, waves of strikes, race riots and terrorist bombings.
The Democrats' collapse in 1920 was the voters' response. It wasn't because of a weak ticket. Cox was a three-term Ohio governor who created the Cox Communications empire; today his 94-year-old daughter is worth $12 billion. His running mate was Franklin D. Roosevelt.
The 2016 Democratic ticket, though perhaps weaker, likely won't fare as badly. Americans these days mostly vote straight tickets. Even in 2008, 46 percent voted for John McCain.
And certainly everyone hopes the nation doesn't suffer disasters like those of 1919 and 1920. But that election is a reminder that the bottom can fall out for a party.
Democratic nominees have received at least 48 percent of the vote in the last five presidential elections, going back 20 years. Obama has left them stronger than ever in central cities and university towns.
But the party has receded elsewhere. Bill Clinton in 1996 had better percentage margins than Barack Obama in 2012 in 36 states. A ticket weaker than Obama in central cities and weaker than Clinton elsewhere might fall well below 48 percent.
I don't think a Democratic nightmare scenario is likely. But some numbers point in that direction.