Democrats dreaming of retaking Congress this November just got their best news of the election yet — and it’s not Donald Trump doing anything new and bizarre.

On Wednesday, the Public Religion Research Institute and Brookings Institute released a poll that showed Hillary Clinton up 15 points over Trump. But the poll’s more important finding — we’ve known Clinton is beating Trump for months — had to do with the battle for House.

It’s very difficult to figure out who is set to win the House — unlike the presidential and Senate races, there are very few public polls of individual districts. Instead, experts rely on what’s called a “generic ballot,” which asks voters if they’d prefer a generic Democrat or a generic Republican (with no names attached) to get a sense of which party is more popular in the country overall.

Historically, this metric has probably been one of our best ways for guessing what will happen in House races across the country. And PPRI/Brookings found that the number has zoomed in the Democrats’ direction — the poll found Democrats leading in the generic ballot by 12 points.

Wow. Biggest news here isn’t anything RE presidential race. It’s the 12 point Dem lead on the generic Congressional https://t.co/CQXh3p9a0W — Dana Houle (@DanaHoule) October 19, 2016

That number — even though it’s a huge lead — doesn’t imply a huge majority for House Democrats. But it does put them in striking distance. Earlier this campaign, Emory political scientist Alan Abramowitz created a model based on the “fundamentals” — things like the state of the economy and the president’s approval rating — to game out the state of the House race.

He found a 13-point advantage in the generic ballot would translate into a Democratic gain of more than 30 seats — enough to give Nancy Pelosi her gavel back:

For now, this poll is still an outlier

The best election gurus, like Dave Wasserman at the Cook Political Report and John Sides of the Washington Post, have been generally skeptical of the notion that the House is in play.

They note, correctly, that redistricting has created a fortress of extremely safe Republican seats, and that Democrats would essentially have to sweep all close races to have a shot. Moreover, despite Donald Trump’s implosion in the polls, Senate Republicans are polling pretty well. That’s at least a sign that voters may dislike the Republicans’ toxic presidential candidate, but are still going to vote for Republican congressional candidates.

If Trump was really dragging the rest of the party with him, you’d expect to see Republican popularity cratering in the generic ballot. But, for most of the campaign, Democrats’ “generic ballot” popularity has not been that strong.

As the Washington Post’s Aaron Blake noted on Monday:

There's real reason for GOP optimism that Trump won't ruin their year completely. The so-called generic ballot … still favors Democrats by only a small margin: three points in both the Post-ABC poll and NBC News-Wall Street Journal poll, among likely voters. That same Democratic edge on the generic ballot is actually down from six points in last week's NBC-WSJ poll. Put plainly, these generic ballots are unremarkable and don't suggest a big Democratic wave ahead.

We should be clear: Today’s PPRI/Brookings poll is still an outlier. Two other recent polls — one conducted by Bloomberg and another by George Washington University — found Democrats up by only about 5 points.

But Barry Burden, a political scientist at the University of Wisconsin, told me earlier this month that while Democrats might not be nationally popular enough right now to see a coming wave election, it’s still early. In 2006 and 2010, Burden noted, the party that caught the landslide didn’t pull far ahead in the generic ballot until very late in the fall.

"The presidential campaign has been such a circus that most of voters’ attention has been focused on that," Burden said. "I’m not sure exactly if we know yet what voters want to do with Congress."

If the 12-point advantage held, it really would be huge. Not since 2006 and 2008, when Democrats painted the map blue, have they done this well in the “generic ballot.” Even then, their high point was an 11-point lead in 2008:

And then there’s another factor working in Democrats’ favor: We’ve never seen a presidential campaign like Trump’s.

There are lots of ways Trump is creating a fundamental asymmetry at the presidential level whose impact we can’t gauge on the down-ballot races. Some political scientists, for instance, have found that "field offices" can add several percentage points in the presidential election, according to Burden. (Trump has hardly set any up compared with Clinton.)

They’ve found most presidential candidates bolster down-ballot races by encouraging their party’s voters to cast early ballots. (Trump isn’t really doing that.) Burden notes that in most presidential election years, campaigns deploy famous and well-liked surrogates to drum up support in certain states to get them to the polls. (Trump is mostly still arguing with them.)

"All of our models, and so much of what we know, suggest that the House Republicans should be fine," Burden says. "But all of the models also presume that parties operate the way parties have operated in the past. And the trouble with Trump is that he’s changing everything at once."

Watch: Democrats are in trouble even if Clinton wins