Republicans searching for a silver lining in the returns from the nail-biting special congressional election in western Pennsylvania may as well admit it. There isn’t one.

True, their candidate Rick Saccone came tantalisingly close. So much so he was holding off conceding to his Democrat opponent Conor Lamb, who had gone ahead and claimed victory despite leading with only 0.03 per cent – or about 600 votes – across a district that stretches from the suburbs of Pittsburgh, to coal and farming country on the West Virginia border.

They may try to hide behind the fact that Pennsylvania’s 18th District is set to vanish anyway as the state’s entire congressional map is redrawn. Whoever is eventually confirmed as the victor will have to resume campaigning almost immediately ahead of the midterm elections in November, and for votes in a seat that will look very different from the one he just competed for.

They could even try to argue that Saccone, a veteran of the state legislature, was simply a lousy campaigner, and that Lamb was so effective he must be an outlier. And it’s true that the one was as awful as the other was terrific.

But here’s the thing: so deeply red has this seat historically been, that the party should have held onto it fielding a blind St Bernard with a lisp. Indeed, it was judged so safe that the Democrats didn’t even bother contesting it in the last two election cycles.

So let’s say enough errant votes do turn up, possibly in a recount, that Saccone is able to scrape by after all and deny the victory that Lamb says is his. What would that change? Nothing at all, really, because he should have romped home and didn’t.

And that means just one thing: the fear already stalking Paul Ryan and the rest of the Republican leadership, that they are on track for a drubbing in the midterm elections, is now more than that. It’s a virtual certainty.

You may say that one cow in a pasture of 435 (the total number of seats in the House) sitting in the grass, doesn’t necessarily mean rain is coming. A lot could happen to change the political landscape between now and Election Day on 6 November.

Yet, everything about this one little race should pitch Ryan et al into a full-blown panic. Ryan told his cohorts on the Hill the result was a “bit of a wake-up call”. That’s funny. He’s great at Midwestern understatement.

Ryan knows the legacy of his leadership may now be squandering the majority his party won in the House back in 2010. A Democrat take-over of the chamber would be as disastrous as it sounds. All the legislative goals of the party and President Trump would be swept into the ditch, unless it was something that could attract Democrat support, like, say, a big infrastructure bill.

Again, are we over-interpreting this? First, remember that history tells us that in midterms there is almost always a voter rebellion against the party in charge. That’s part of what happened to Barack Obama eight years ago.

Clinton got a pummelling in 1994, two years after the start of his first term, when the “Republican Revolution” led by Newt Gingrich gave Republicans a net gain of 54 seats. To retake the majority this year, Democrats need only a 24-seat pick-up.

Even before this latest debacle, Republican House members were announcing their retirement from Congress at a rate far exceeding other recent Congresses. If they were seeing a Democrat wave coming, it was partly because of what happened late last year in states like Virginia and Alabama. Democrats won the governor’s office in the former, and a Senate seat in the latter.

And now this. Trump won Pennsylvania’s 18th District by 20 points in 2016, reason enough to imagine that any Democrat would have faced impossible odds stealing it away. Moreover, the President visited twice in recent weeks, precisely to make sure none of that enormous margin leaked away. He also used his Twitter account liberally to cajole his supporters into turning out for Saccone, and spurning Lamb.

Trump says he wants to spend as much time as possible campaigning for Republicans. Very few will now want him anywhere near their districts.

But here is what’s worst for Ryan: what are his candidates meant to run on this autumn? What is the party’s overriding policy message going to be? “Vote for us to support Trump” won’t stick if his approval ratings stay where they are now. How about, vote for us because of his job-saving import tariffs? Or vote for us because of the historic tax-cutting law we just passed?

Both were tried in Pennsylvania and neither worked. Outside conservative groups spent nearly $10bn (£7.16bn) on TV spots for Saccone: more than twice that spent by Democrats. At first they were all about the tax reform, but that moved voters not a jot; towards the end of the campaign, they had given up touting the tax cuts altogether. Meanwhile, if the steel tariffs were going to excite folk anywhere it should have been here, the heart of America’s steel country. Again, no dice.

The Democrats, meanwhile, have grasped something vital. Insofar as they are able – and the party cannot control the process completely – they will be tailoring candidates to the districts they will compete in. There will be no ideological purity tests this year (sorry Elizabeth Warren and Bernie Sanders). Lamb was a former marine who supported tariffs himself: who separated himself from Nancy Pelosi and who ran to the centre on guns and abortion.