On Tuesday in Massachusetts, there was another dramatic win for a Democratic insurgent, as Boston City Councilor Ayanna Pressley defeated Rep. Michael E. Capuano, who has been in Congress almost two decades. Pressley is all but guaranteed to win the seat in November.

If you’re a Republican, you probably hope that this and other primaries represent Democrats nominating a bunch of extremists who will push their party so far to the left that independent voters will never support them, and the result will be more Republicans getting elected.

But that’s not what’s happening. There is something revolutionary afoot in the Democratic Party, but it’s more of a careful and long-overdue revolution than a violent upheaval.

First, we have to acknowledge that as interesting as a primary like this is, only four members of the House — two Democrats and two Republicans — have lost this year. The Republicans, Mark Sanford of South Carolina and Robert Pittenger of North Carolina, lost mostly because they weren’t seen as sufficiently pro-Trump. The Democrats, Capuano and Joe Crowley of New York (who lost to Alexandria Ocasio-Cortez), fell not because of any ideological apostasy (they’re both strong liberals) but because as middle-aged white guys representing diverse districts, they had trouble when faced with young, dynamic minority women who ran potent grass-roots campaigns.

Even if Pressley’s and Ocasio-Cortez’s victories are the exception when it comes to ousting incumbents, there has been a dramatic shift this year in who’s running for Congress — but almost entirely on the Democratic side. Cook Political Report analyst Dave Wasserman sums it up:

That is an absolutely stunning statistic. Among other things, it shows that the Democratic Party is at least approaching representation that looks like its own voters, while Republicans have it right on race but not on gender.

We can see why using the Pew Research Center’s recent study of people who voted in 2016. While the Trump electorate was 88 percent white, it was close to evenly divided among men and women, which means that women are significantly underrepresented among Republicans in Congress. Only six of the 51 Republicans in the Senate are women, compared with 17 of the Democrats’ 49 senators.

Republicans have 17 incumbent women running for the House, plus 35 women nominated as challengers or for open seats. So their numbers may increase after the election. But compare this with Democrats: 54 incumbent women running, and 138 women nominated as challengers or for open seats (more data here).

The Democratic electorate is dramatically different from the Republican electorate. According to Pew, 60 percent of Hillary Clinton’s voters were white, 19 percent were African American, 14 percent were Hispanic, and 7 percent were Asian or some other race. That’s very similar to the country’s racial/ethnic makeup as a whole: According to the most recent census data, we’re 60 percent white, 13 percent African American, 18 percent Hispanic, and 6 percent Asian or Pacific Islander.

The “firsts” we’re seeing this year are each important in and of themselves — first African American woman elected to Congress from Massachusetts, first African American woman from Connecticut, first Muslim woman, first Palestinian American, and so on. But what’s more significant is that Democratic voters seem eager to elect more diverse representatives. That could be just a function of this unusual year, but I doubt it.

Republican voters, on the other hand, don’t seem to see the gender imbalance in their representatives as much of a problem. They’re perfectly happy to have more women run on their ticket but they don’t exactly see it as an urgent priority that requires a concerted effort to address. As for nonwhite candidates, they’re glad to have them when it’s possible, but there just aren’t that many nonwhite Republicans out there who’ll run for office. There are likely never going to be more than a few African American and Hispanic Republican officeholders here and there, at least not in the near future.

As for the question we started with, there’s little indication that the new crop of Democratic representatives is going to shift the party more left than it would have gone anyway. Yes, there are some new, young, minority Democratic candidates advocating things such as single-payer health care. But that’s what the older Democrats who are going to run for president in 2020 are advocating, too. The whole party has moved, no matter which of its candidates winds up winning in November. Nevertheless, there are strong progressives losing some Democratic primaries as well, not to mention some more centrist Democrats, such as Conor Lamb and Kyrsten Sinema, performing extremely well.

Keeping that big tent together if and when Democrats take power is going to be a real challenge. But at least they’ll be able to say that as the more diverse of the two parties, they’re finally catching up to their own voters.

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