Whatever happens in the first round of voting in the special election in Georgia’s Sixth Congressional District on Tuesday, it seems like a safe bet that the result will get a fair amount of national attention because of what it may tell us about the 2018 midterm. But before getting into what those lessons may be, let’s remember that this is a special election — and thus it features special circumstances.

Here are a few:

The format for this election is different than most other races: It is an all-party primary where there will be a runoff unless one candidate gets more than 50% of the vote. That means all of the candidates regardless of party run together in the same election. This is not how almost all House elections will be decided next year: With the exceptions of California, Louisiana, and Washington, all of which use some form of “jungle primaries” in their elections, other states will use a traditional primary and general election format next year. That includes all of the House races in Georgia — the jungle primary being used for this race is just used for special elections. And even in California and Washington, there still is a general election between the top two finishers even if one candidate exceeds 50% in the primary. So this electoral format won’t be replicated anywhere outside of Louisiana in November 2018.

There are a whopping 18 candidates in this election, and 11 of them are Republicans. That includes several strong GOP contenders, such as former Georgia Secretary of State Karen Handel, former Johns Creek City Councilman Bob Gray, and former state Sens. Judson Hill and Dan Moody, among others. Meanwhile, there is only one viable Democrat, former congressional staffer Jon Ossoff. Polling indicates that Ossoff is effectively guaranteed at least a spot in the runoff, and he has an outside chance to win outright — a possibility that this unusual election format allows him. The Republican field, meanwhile, is bunched with a number of contenders in high single or low double digits. So Ossoff can stay above the fray while the Republicans fight among themselves. Republican outside groups seeking to prevent Ossoff from winning before the runoff have spent millions on attack ads against Ossoff, some of which ask voters to only blandly “vote Republican” on Tuesday because, for the most part, these groups are not endorsing a specific candidate.

While there have been a handful of state legislative special elections this year, and one House special (in Kansas’ very Republican Fourth District, where the Democratic candidate strongly overperformed the district’s partisan lean on Tuesday but did not win — more on that below), Democrats have circled this race for months as perhaps their first real opportunity to strike back at President Donald Trump and Republicans after their surprise victories last fall. Ossoff has emerged as a dynamite fundraiser, raising an unprecedented $8.3 million so far, which is a historic number for any House candidate. Other Democratic candidates will benefit from the small donors who have fueled Ossoff next year, but they won’t be raising such amazing sums of money because there will be much more competition for donor dollars when all 435 House districts will have elections.

The suburban Atlanta seat is historically Republican. Its former occupant, now-Secretary of Health and Human Services Tom Price (R), never failed to win less than 60% in his seven general election victories. Mitt Romney carried the seat by 23 points in 2012. But Trump only won it by a point and a half, and it is the kind of district — suburban, well-educated, affluent, and somewhat diverse — that Democrats have increasingly targeted in recent years and where Trump came up well short of usual Republican showings. Of all the Republican-held districts in the country, in only one other district did Hillary Clinton run further ahead of Barack Obama’s 2012 showing — TX-7, a suburban Houston seat held by Rep. John Culberson (R). That GA-6 swung so hard in 2016 at the presidential level makes it something of an outlier too, even though nearly half of all congressional districts experienced at least some significant degree of change in 2016.

This district is open, which won’t be the case in the lion’s share of House elections next year. In the post-World War II era, an average of about nine out of 10 House incumbents sought reelection in any given cycle. So we’d expect most House elections, and most competitive House elections, to feature incumbents next year. Generally speaking, incumbents have at least a little bit of a built-in advantage against challengers, an advantage the Republicans do not have in GA-6.

Oh, and this election is taking place a year and a half before the midterm. President Trump is probably a drag on Republicans now — his disapproval rating is roughly 10 points higher than his approval rating, which is a bad sign for his party’s midterm performance historically — but it’s impossible to say what his standing will be in a year and a half.

So, to sum it up, the GA-6 special is indeed special: It uses an election format that hardly any other 2018 races will use; it features only one prominent Democrat who has used his unique position to harness an immense fundraising base while a giant Republican field fights for scraps; it is taking place in a district that changed dramatically at the presidential level from 2012 to 2016 in the Democrats’ favor; and it is an open seat.

This is all a way of saying that those who project the GA-6 outcome, whatever it is, onto the still-distant 2018 midterms do so at their own peril. History tells us that these special elections can be a harbinger of the future, although there are plenty of examples illustrating when special elections provide misleading or mixed signals of what is to come.

Greg Giroux, a political reporter for Bloomberg and one of the nation’s leading experts on electoral politics, has helpfully compiled every House special election held since the start of John F. Kennedy’s presidency in 1961. There have been 247 special elections in the five and a half decades since then, including Tuesday’s special in KS-4. Roughly a fifth of those elections — 47 of 247 — saw a party change, and generally speaking, the party changes broke against the White House. Of those 47 party changes, 35 of them involved the party that did not control the White House winning the seat from the president’s party, while the other 12 flipped in favor of the president’s party.

This makes some sense, given what history tells us about midterm elections. The president’s party typically loses ground in midterms, and a special election essentially amounts to a mini-midterm election: Turnout is significantly lower than a presidential election and the party that doesn’t hold the White House can be more motivated to vote.

It’s easy to find times when a special election party change seemed suggestive of an upcoming partisan wave in favor of the party that did not hold the White House. Here are some examples:

As Richard Nixon’s presidency was collapsing amidst the Watergate scandal in 1974, Democrats won five special House elections in seats previously held by Republicans — a series of Democratic wins that “helped convince Republicans that Nixon needed to resign,” according to the Almanac of American Politics. Nixon would indeed leave office in August 1974, but that didn’t stop Democrats from netting 48 House seats and four Senate seats that fall, padding their majorities in both chambers in the early months of Republican Gerald Ford’s presidency. Two of those Democratic victories stand out. After Ford ascended from the House to the vice presidency following the resignation of scandal-plagued Spiro Agnew in 1973, Richard Vander Veen (D) surprisingly carried his typically Republican Grand Rapids-based district. A couple of weeks earlier, John Murtha (D) won a very close election in a Western Pennsylvania special. Murtha would go on to a long career in the House, but in the immediate aftermath of his victory by just one-tenth of a percentage point neither party knew quite how to react: Many expected Murtha to win by more despite the fact that he was the first Democrat to win the seat in a quarter-century: “The question most puzzling to Democratic strategists here is why Mr. Murtha’s margin of victory was so small — the slightest any one could remember in the 12th Congressional District’s modern electoral history,” the New York Times reported. In fact, the Republican National Committee chairman — a fellow by the name of George H.W. Bush — told the Times that the narrow result meant that “Republican chances for the rest of the year are greatly enhanced.” That ended up just being spin, but the result was not a clear indicator at the time: Murtha’s win was just the first of the five aforementioned Democratic special election takeovers in the first half of 1974.

More recently, Republican victories in two long-time Democratic districts in May 1994 special elections in Kentucky and Oklahoma provided some early signals of the GOP wave to come, when Republicans captured both the House and the Senate in President Bill Clinton’s first midterm. Democrats would also pick up three Republican seats in the first half of 2008, including one held by departing former House Speaker Dennis Hastert as well as two dark red seats in Louisiana and Mississippi. Democrats added to their House majority later that year.

AAnd sometimes a seat that does not flip can be taken as an indicator. In March 2014 — the most recent House special election that elicited major national attention — David Jolly (R) won a Tampa Bay-area House district against Alex Sink (D), a former state chief financial officer and gubernatorial nominee who appeared to be a favorite. Republicans would add seats to their already-substantial House majority that fall and win control of the Senate by running against an unpopular President Barack Obama. In 2005, there was a close call in the heavily Republican southwest Ohio House district future-Sen. Rob Portman (R) vacated to join President George W. Bush’s administration. That seemed like an early suggestion of GOP troubles the following year, when Democrats won the House and the Senate.

But in other instances, special elections can provide misleading or mixed signals:

Democrats won two Republican-leaning seats in special elections in Kentucky and South Dakota in the first half of 2004, but Republicans ended up reelecting George W. Bush in a competitive presidential election and making small gains in the House and Senate.

Democrats won three nationally-watched special elections in 2009 and early 2010: They held two vulnerable seats in New York and Pennsylvania — the latter was the one held previously by Murtha, who died in 2010 after more than 35 years in the House — and they flipped a historically Republican district in upstate New York thanks in large part to a split in the GOP. These Democratic victories perhaps suggested that Democrats could weather the storm in 2010 — but of course Republicans ended up netting 63 House seats, winning the lower chamber and making big gains in the Senate.

In May 2011, Kathy Hochul (D) scored a surprising upset in a Republican-leaning seat in Western New York, which at the time suggested Democrats could run nationally against an austere budget proposal by Rep. Paul Ryan (R), the future House speaker who at the time was becoming one of the leading voices of the new Republican House majority. Later that year, Bob Turner (R) scored a similarly surprising upset in a Democratic-leaning New York City seat previously held by Anthony Weiner (D), who was forced from the House in what would become a series of social media-induced embarrassments. Hochul and Turner both ended up being done-in by new district maps in New York: Turner didn’t even bother running for reelection after his district was dismantled (he lost a primary for a Senate nomination that wasn’t really worth having in 2012) and Hochul, currently New York’s lieutenant governor, lost a narrow reelection to now-Rep. Chris Collins (R), who has become nationally prominent as a Trump ally and surrogate. The 2011 New York House swap perhaps presaged what would be a relatively status quo House election: Democrats netted a mere eight seats despite Obama’s reelection, on a national House map that had become generally more Republican thanks to the GOP’s 2010 victories and subsequent redistricting strength.

So as we assess GA-6, it’s certainly possible that Ossoff could win outright on Tuesday and that Democrats could end up having a disappointing midterm anyway. Or he could lose decisively in a June runoff and Democrats could come back and have a massive wave election next year. It’s ultimately just one election held amidst unusual and, dare we say it, special circumstances.

We’re calling GA-6 a Toss-up, a designation we applied to the race roughly two weeks ago after the National Republican Congressional Committee sounded the alarm bell and started aggressively spending money in the district. That’s in addition to the millions the Congressional Leadership Fund, a Super PAC that is close to Speaker Ryan, has also spent in the district. Since then, Ossoff’s huge fundraising has come to light, as have early voting statistics that seem to indicate heavy Democratic interest in the race (although Republicans, who have more candidate choices and thus perhaps waited longer to vote, are catching up).

So there’s a lot of uncertainty about the outcome: Polling, typically spotty in House races, generally shows Ossoff in the low 40s. If that’s all he gets in the first round of voting, and the combined Republican vote is over 50%, one would assume that Ossoff’s general election opponent would start with the upper hand: After all, the first round results are better than any poll — they are actual voting results that can be a preview of the runoff on June 20, if there is one. However, if Ossoff’s vote and the scattered votes for the four other Democratic candidates add up to a total approaching 50% (say, 45% or more), it may indicate that the runoff should be quite competitive. Obviously, a first-round win by Ossoff would be noteworthy because he would have exceeded Clinton’s 46.8% 2016 share significantly — and blown recent previous Democratic House performance in the district out of the water. Another factor: As of now, Ossoff and Democrats have not been attacking the Republicans because it’s anyone’s guess how the first round will play out, while outside GOP groups have been hammering Ossoff, hoping to drive down his numbers (and while Ossoff has been running lots of positive ads on his own behalf). Ossoff and national Democrats may be preparing to drop the hammer on whichever Republican emerges from the first round, again assuming Ossoff does not win outright on Tuesday. In other words, the dynamic changes on Tuesday in advance of a possible runoff: The GOP survivor goes from running against his or her fellow partisans to running against Ossoff, while Ossoff can shift into attack mode because he would have a clear opponent.

Perhaps the more useful way to interpret the results in GA-6, whatever they may be, is to put them in context of the other special elections that have happened so far in state legislative races as well as the KS-4 special.

In 10 special elections so far — nine state legislative races and the KS-4 U.S. House special — the Democratic candidate has improved on Clinton’s 2016 margin in eight of them. Across all 10 races, the average net improvement has been 11 points. Now, this is a small sample size, and the results vary dramatically — ranging from a Democrat doing a net 22 points worse in a deeply Democratic state Senate district in Connecticut all the way to one who did a net 34 points better in an Iowa special House election in a Democratic-leaning district. (Daily Kos Elections and Huffington Post are keeping track of these races.) If this trend continues throughout 2017 as the data accumulate, this could be suggestive of broader GOP problems and intensified Democratic enthusiasm.

Indeed, back during the last midterm cycle, the always-perceptive Sean Trende of RealClearPolitics (and a contributor to our new book on the 2016 election, Trumped) identified consistent Democratic underperformance in elections conducted in 2013. That year, the early tea leaves correctly suggested the midterm outcome — a weak Democratic performance in 2014 defined by poor Democratic turnout in many places. The 2017 tea leaves may not be such an accurate predictor, but at least looking at all the races as a group helps iron out the unusual circumstances of a given race — and, as noted, GA-6 features a lot of unique characteristics — and tells us more about the broader environment.

If that’s the way to project special election performance forward to the midterm, then GA-6 is but one data point that may or may not confirm national trends. So by all means, pay attention — but not just to a single race like GA-6. Remember Lester Freamon’s advice from The Wire: “All the pieces matter.”

And that includes many pieces that go beyond special elections: national House generic ballot polling, the president’s approval rating, candidate recruiting, and retirements. It may be on those latter two factors where special elections exert some influence — if the accumulated results suggest overperformance by one side, that party could have an easier time finding candidates, while incumbents from the party on the wrong side of the results could give stronger consideration to spending more time with their families.

Housekeeping: Other races and ratings changes

Rep. Tim Walz (D, MN-1), who saw his swingy district move from one that Barack Obama won by a point and a half in 2012 to one that Donald Trump carried by 15 in 2016, recently decided to run for governor of Minnesota. Without a proven incumbent in the race, this seat becomes a top GOP pickup opportunity, so we switched the rating there from Leans Democratic to Toss-up. Republicans also must be hoping that Rep. Rick Nolan (D, MN-8) joins Walz in the gubernatorial race — he reportedly is strongly considering joining the already-large Democratic primary field. If he does make that leap, that will create another Toss-up race in Minnesota and improve the GOP’s odds in another district the party was already planning on targeting in 2018 (if Nolan opts against a gubernatorial bid, his race will remain at Leans Democratic for now). Just a few Republican pickups in seats where Trump significantly outperformed Mitt Romney’s 2012 showing, which was the case in both MN-1 and MN-8, could complicate Democratic hopes to net the 24 seats they need to win control of the House next year.

Despite Rep.-elect Ron Estes’ (R) underwhelming performance on Tuesday, KS-4 starts as Safe Republican for the 2018 general election. Democrats have many other more competitive districts to target next year. Two of those Republican-held seats could be another open Kansas seat, KS-2 (held by retiring Rep. Lynn Jenkins), as well as OH-1, a suburban Cincinnati seat held by Rep. Steve Chabot. Trump won both districts, but Democrats held prior versions of these districts last decade, and they could be competitive if Democrats can find strong candidates in each. We’re listing both as Likely Republican now instead of Safe Republican. A factor in the closer-than-expected KS-4 special — Estes won by seven after Trump carried the district by 27 in November — is that Kansas state government, led by Gov. Sam Brownback (R), is deeply unpopular, and the state has a long history of infighting between moderate and conservative Republicans. Local wrinkles might have made KS-4 more competitive than it otherwise would have been, and the same thing could impact KS-2. Trump carried OH-1 by seven and KS-2 by 18, so it’s not like these are obvious Democratic targets, and a Likely Republican rating doesn’t indicate immediate danger for the GOP in these seats. But the map might open a bit for Democrats if Trump’s numbers don’t improve.

Rep. Ed Perlmutter (D, CO-7) opted to run for Colorado governor instead of seeking a seventh term in his suburban Denver seat. The district was swingy at one time but it has trended Democratic in recent years: Hillary Clinton won it by 12 points, a little bit down from Barack Obama’s 15-point win in 2012 but still several points more Democratic than the nation. We’re keeping this open seat at Safe Democratic for now, but if Republicans field a competent challenger it has the potential to move to a more competitive rating.

President Trump appears poised to name Rep. Tom Marino (R, PA-10), as national drug czar, which will eventually prompt another special election, this time in his dark red Northeast Pennsylvania seat. Trump carried the seat by 36 points in 2012, 66%-30%, making it significantly more Republican than even KS-4. Again, watch the margin here — it’ll be another special election data point — but there’s little reason to think the race will truly be competitive. It remains Safe Republican.

Table 1: House ratings changes

*Note: We announced the changes in MN-1 and GA-6 on March 27 and March 30, respectively, on Twitter, but we had not previously mentioned them in our Crystal Ball newsletter. To stay up to date on our ratings changes, please bookmark our Ratings Change page.