You’ve seen the numbers: In 2016, Donald Trump carried Pennsylvania’s 18th Congressional District by 20 percentage points. In 2012, Mitt Romney carried it by 17 points. It is the heart of Trump country, overwhelmingly white with strong working-class roots.

Yet after Republicans invested more than $10 million in this week’s special election, vastly outspending the Democrats, after Trump and Vice President Mike Pence traveled to the district to stress its importance to their cause, after doing everything they could imagine to hold that seat against a rising Democratic wave, Republicans narrowly lost the 18th District Tuesday.

To fully explain what that loss might mean nationwide come November, let me offer a few more numbers to put it into context:

  • After last night's apparent victory by Conor Lamb, Democrats need 23 more seats to take control of the House.
  • Prior to Tuesday's results, 47 Republican-held House seats were already judged "vulnerable" by the well-respected Cook Political Report.
  • That number will now grow. More than 110 Republicans hold House seats that they won by less than the 20-point swing that we saw this week in the 18th District. Democrats won't win all of those seats come November, or even most of those seats. But if they win just one out of four or five of those seats, they will retake the House.
  • Forty-two House Republicans have already announced their retirements, the highest total in 90 years. With a blue wave rising, that number is now likely to grow as well.
  • At this point in his presidency in 2010, Barack Obama had a job-approval rating of 48.5 percent, according to the polling average at Real Clear Politics, yet in the midterms later that year, his fellow Democrats went on to lose 63 House seats. According to the RCP polling average, Trump has a job-approval rating of 41.1 percent.

Publicly, national Republicans are trying to underplay the importance of  Tuesday’s loss, as they must, and their spin takes two basic approaches.

First they argue that their candidate was not exactly a ball of fire, and they’re right. As his closing argument on election eve, for example, Rick Saccone ranted that Democrats not only hate Trump, they “have a hatred for our country and I’ll tell you some more — my wife and I saw it again today -- they have a hatred for God.”

That’s not the kind of rhetoric that goes over well in a general election, but it has become almost necessary to win the GOP nomination. Pennsylvania Republicans chose Saccone not despite that rhetoric but because of it. They put him up as the best they could offer, as their spokesman for their values and priorities, just as Alabama Republicans put up Roy Moore as their champion, and the results were similar.

If your internal party dynamics keep producing such extremists as candidates, maybe that’s not an excuse for poor results. Maybe that’s the problem.

The Republicans’ second explanation for their loss is that Lamb did not run as a national Democrat, that in some ways he ran more like a Republican.

Again, that has a veneer of truth. However, if Lamb ran as a Republican, it was as a Northeast Republican from 30 or 40 years ago, as a pragmatic, non-ideological candidate who doesn’t insult the intelligence of voters with anti-science screeds and who doesn’t feel the emotional or political need to bash immigrants and minorities.

Put another way, Lamb ran as the kind of Republican that the GOP has spent a generation systematically evicting from its ranks, replacing them with likes of Saccone.

Furthermore, no Republican would have embraced and defended Obamacare, as Lamb did. Campaigning in a heavily Republican district, he reminded voters over and over again that the Affordable Care Act has “provided affordable coverage to more than a million Pennsylvanians who were previously uninsured.”

“Our representatives in Congress should be working together to build on that progress,  fix what isn't working, and make the law better,” Lamb says on his website. “Instead, Republicans in Congress spent the past year trying to take health insurance away from people with no plan to replace it.”

A Republican also would not have attacked the GOP tax cuts as a giveaway to the rich. Lamb did so directly, and like his health-care argument, it resonated. Early in the race, outside Republican groups had made Lamb’s opposition to the tax cuts a central theme of their advertising campaigns, believing that it would be key to victory not just in the 18th but nationwide.

Toward the end of the campaign, responding to internal polling, those same GOP groups went silent on the tax cut because they realized that their single legislative achievement was backfiring with voters.

That’s a critically important lesson. Sixteen months ago, Trump ran as a populist, promising to protect Social Security and Medicare, promising to take the side of working people over the economic elite, promising to stand up against Wall Street and corporations.

That is not how he and his fellow Republicans have governed, not by a long shot.

To the contrary, Trump has basically handed the country to the very same elite that he railed against. The massive deficits created by tax cuts for the rich are now regularly cited by Republicans as an excuse to cut Social Security, Medicare, health care and other safety-net programs, and Lamb reminded voters of that dynamic at every opportunity

The argument clearly struck home in the 18th District, which doesn’t surprise me. I went to high school and part of college in that district, and from what I can tell it hasn’t changed much. It remains culturally conservative, but thanks to its industrial, working-class legacy, many of its voters instinctively takes the side of the little guy over the boss. Even much of its suburban, college-educated electorate is just a generation removed from the steel mills, and it is still part of their family identity.

In 2016, Trump used a populist style to advocate a supposedly populist agenda, and people responded, in the 18th and elsewhere. In 2018 the populist style remains, but for those who care to see, the true agenda has been exposed.

As a result, the response from voters looks like it may also change dramatically.