Normally a by-election in a non-descript Pennsylvania congressional seat would not attract much attention.

But the contest for the 18th district in that state became much more than a head-to-head between Republican Rick Saccone and Democratic candidate Conor Lamb.

Just over a year ago, President Donald Trump cleaned up in the largely white, working class area – a mix of urban and rural voters.

He won by a whopping 20 points.

Now, it appears the Democrats may have just scraped a historic victory, although there may still be a recount ahead at the Republicans’ request.

If the Democrats do carry the win, it will be a stunning turnaround in such a short time.

Of course one election was for the President, and this was a local affair, but still they’re beside themselves with the possibilities.

Project this dramatic reversal of voting intentions on November’s mid-term elections and the Democrats can almost touch the holy grail; regaining control of Congress and perhaps even the Senate.

And if you average the swings in other by-elections since Mr Trump was elected, you have a 16-point turnaround.

That’s more than enough to do the job, although a lot can happen between now and November that will have Republican lawmakers very nervous.

Even Speaker Paul Ryan is history by that calculation.

He had a very simple explanation for the overnight result in Pennsylvania; Democrat candidate Conor Lamb carried Republican values – a lamb in wolf’s clothing.

Certainly Lamb is anti-abortion, pro-guns and is critical of the Democratic Party leadership. But he’s also a marine, young and good looking.

Failed Republican candidate, Rick Saccone, is none of those.

Mr Lamb’s victory would have major implications for the Republicans. Photo: Getty

What compounds the pain for Mr Trump is that he campaigned hard for Mr Saccone, speaking at a huge rally just last week.

It appears Mr Trump invested in a loser, although he reportedly called the candidate “weak” in private.

He won’t like the optics of a loss.

The special Trump stardust liberally bestowed on Mr Saccone failed to glitter.

What is dangerous for the President is that Republicans who have remained silent on his more controversial decisions and opinions may feel freer to speak up.

After all, if he can’t help them win their seats, his power and value is diminished.

Expect a less compliant party.

Not that Mr Trump appears to fret about his popularity on the Hill.

He’s built his powerful narrative of Washington as a swamp full of alligators … Democrats and Republicans.

If some of his own now turn on him, or at least disagree on specific policies, he will likely paint them as the same Washington insiders dragging the USA down.

There are lessons for everyone from this race.

Pick great candidates who reflect local values and aspirations. Don’t count on a president saving mediocre aspirants. And get your supporters out on polling day.

With non-compulsory voting, it made all the difference in this district, and will do so again.

Is the President damaged by this result? He certainly hasn’t emerged enhanced.

Donald Trump loves to simplify things … politics characterised as a game of winners and losers.

Today, by association, he’s friends with failures. And that will hurt.

-ABC