Get ready for an outbreak of headlines tomorrow about how Donald Trump portends the crackup of the Republican Party. Many of the stories have already been written. They await only a successful effort by Democrat Jon Ossoff to take the seat for Georgia’s Sixth Congressional District that Republicans have held since Newt Gingrich won it back in 1978.

In a special election that has spawned a thousand lessons for our politics, the most obvious goes unmentioned: You can make any House seat competitive if you’re willing to make the race for it the most expensive in American history. Yet somehow the scolds who are always moaning about the corrosive effect of money in politics have gone silent about the $23 million Mr. Ossoff raised—most of it from donors outside the state.

Certainly a Democratic capture of a seat held by a Republican, Tom Price, who now serves in Mr. Trump’s cabinet, would lift Democratic spirits. Still, the race has been overhyped. While it does offer lessons for both Republicans and Democrats, in general these are not the ones getting all the ink.

Start with the Republicans. Back in April, Karen Handel beat 10 other Republican candidates (all but one of them men) in the initial April 18 election. Mrs. Handel is a fairly standard-issue Southern conservative well known in the district from her prior runs, including unsuccessful recent bids in GOP senate and gubernatorial primaries.

Against Mr. Ossoff her greatest liability has less to do with her than with President Trump. Special elections frequently become referendums on the incumbent party. That’s exactly what Mrs. Handel is now facing from a Democratic rival who got his initial boost from an online campaign based on the pitch “Make Trump Furious.”

Mrs. Handel has tried to steer a middle course on Mr. Trump. Unlike some of her GOP rivals, who fully embraced him in the April contest (and lost handily), she’s been more measured. Although Mr. Trump held a fundraiser for her and recently tweeted his support for her campaign, she tries to avoid mentioning his name on the stump. During a debate with her opponent earlier this month, she insisted she isn’t “an extension of the White House.”

With all this Mrs. Handel’s biggest disadvantage isn’t Mr. Trump but the lack of GOP legislative accomplishments in Washington. The result is that she hasn’t been able to point to legislation as a way of contrasting her agenda with her opponent’s. That leaves her tied to President Trump the Personality rather than President Trump the Leader pushing through a GOP agenda making life better for the American people.

Mr. Trump inadvertently alluded to this dynamic in his own tweet on Monday supporting Mrs. Handel: “The Dems want to stop tax cuts, good health care and Border Security. Their ObamaCare is dead with 100% increases in P’s. Vote now for Karen H.” In fairness, Mr. Trump has been in office only five months, so it’s early days. But if Republicans do not make good on promises like the ones Mr. Trump put in his tweet, in 2018 they will find themselves in a fix worse than Mrs. Handel’s.

But Democrats have their issues too. For one thing, Mr. Ossoff doesn’t even live in the Sixth District. For another, the redness of this district is more complicated than has been presented. In November, Hillary Clinton came within 1.5 percentage points of Mr. Trump. Mr. Ossoff himself came within 1.9 points of winning 50% of the vote in April, which would have spared him a runoff.

The 30-year-old Mr. Ossoff has been changing his tune as well. Making life hell for Mr. Trump may be an excellent slogan for riling up the Democratic base and attracting notice from the national press. But in affluent Republican suburbs where the Democrat will need some GOP votes to push him over the top, the full Bernie probably won’t do it.

So more recently Mr. Ossoff has been playing down the anti-Trump resistance in favor of a more centrist campaign that emphasizes bipartisanship and fiscal restraint. His advantage here is that he’s never held office, so he doesn’t have a record that can be used against him. Meanwhile, the Handel camp is running ads claiming that however moderate Mr. Ossoff may sound in Atlanta, once in Washington he’d be a Nancy Pelosi Democrat.

Plainly the voters are impassioned. Early voting has set a record. In an election hinging on turnout, and at a time when anti-Trump sentiment is at fever pitch, this would appear to be an advantage for Mr. Ossoff.

If he pulls it out on Tuesday, Mr. Ossoff’s victory will no doubt be celebrated from coast to coast as the first clear sign that Republicans are in real danger of losing their House majority in 2018.

But if Mr. Ossoff—with all his millions, with all his volunteers, with all the free media—still manages to lose, will all those telling us the race is a harbinger of things to come ask what that means for the Democratic Party?