In a hypothetical national ballot, Democratic congressional candidates hold a robust 11-point lead over their GOP counterparts, 51-40 percent, among registered voters overall. But winnow down to those who say they voted in the last midterms and are certain to do so again and the contest snaps essentially to a dead heat, 48-46 percent.

That’s in part because the 2014 midterms were so successful for the Republicans, who won the Senate and padded their House majority that year. But past voting is the best predictor of future voting, making it clear that the Democrats will have to change the dynamic to prevail in the next midterms a year off from now.