Democrats overperforming with the real swing voters: those who disapprove of both parties

President Trump helped win the White House thanks to an overperformance among voters who disliked both Trump and Democratic presidential nominee Hillary Clinton in 2016.

But ahead of November's midterms, Democrats are the ones cleaning up with this key constituency, data from the latest NBC/WSJ poll shows.

Democrats have a 30-point advantage over Republicans among this constituency on the generic ballot, a stronger lead than Republicans had during each of their midterm wave years of 2010 and 2014. Fifty-five percent of these voters back Democrats, compared to just 25 percent who back Republicans.

Here's how these voters have responded in past polls in previous years, merging previous polls to get a better look at their preference.

2018 merged NBC/WSJ poll (through June): 50 percent DEM, 36 percent GOP (D+14)

2014 merged NBC/WSJ poll: 51 percent GOP, 24 percent DEM (R+27)

2010 merged NBC/WSJ poll: 49 percent GOP, 23 percent DEM (R+26)

What’s more in our current poll, these voters disproportionately are down on Trump (68 percent disapprove of his job, versus 52 percent of all voters), and they are enthusiastic about the upcoming midterms (63 percent of them have high interest, versus 55 percent of all voters who say this).

As we wrote about last month, Trump's strength among these voters was one of the clues we missed during the 2016 election. And it was an influential clue, as those voters made up 18 percent of the electorate in the merged NBC/WSJ polls in 2016.

So this will be an important voting bloc in the upcoming midterms too, and one among which Democrats will look to ride to a big win.