When Ohio Republican Rep. Pat Tiberi announced in October 2017 that he would resign from the U.S. House of Representatives to become president of the Ohio Business Roundtable, Doug Jones and Conor Lamb were not yet household names, and Democrats had yet to flip a Republican-held seat in a special election. What a difference 10 months make. Ohio’s 12th Congressional District will finally elect Tiberi’s successor on Tuesday, and the race is following a very similar script to previous special elections.

1. The players

Just like in Georgia’s 6th District and Pennsylvania’s 18th District, Democrats in Ohio’s 12th District picked as their nominee a fresh-faced 30-something: Franklin County Recorder Danny O’Connor. And just like in Georgia and Pennsylvania, Republicans chose a 50-something veteran of state politics: state Sen. Troy Balderson.

Like his Democratic antecedents, O’Connor has outraised his opponent in campaign cash, deploying that advantage early on TV ads burnishing his centrist bona fides: He tied himself to Republican Gov. John Kasich and explicitly promised not to vote for Nancy Pelosi for speaker. (Although he may have given back some of that yardage on July 24 when he said on MSNBC that he would support “whoever the Democratic Party puts forward” instead of allowing Republican control of the House.) Meanwhile, in keeping with special–election tradition, some Republicans have anonymously complained about their candidate, although others have publicly embraced him: Kasich (albeit after some initial reticence) endorsed Balderson and cut an ad for him, and President Trump flew in Saturday for a rally.

As in past special elections, Republican super PACs have also come to their candidate’s aid; the top spender is the Congressional Leadership Fund at $3.2 million, and many of its ads have been negative. The good news for Republicans is that they have a sizable overall spending advantage — the Democratic Congressional Campaign Committee is the only progressive outside group that has spent more than $90,000 (investing $630,000).

2. The partisanship

Ohio’s 12th District is traditionally Republican. According to FiveThirtyEight’s partisan lean metric, it is 14 percentage points more Republican-leaning than the nation as a whole. But most districts (along with the one state) that have hosted federal special elections since Trump’s inauguration leaned strongly toward Republicans, and most of those races were decided by single digits. In other words, Democratic enthusiasm, Trump’s unpopularity and the normal mean-reversion tendency of midterm election cycles have transformed normally safe Republican seats into nail-biters.

How will Democrats perform in Ohio’s 12th District? U.S. House and Senate special elections this cycle, by the seat’s partisan lean and final vote margin Year Date Seat Partisan Lean Vote Margin Dem. Swing 2017 April 4 California 34th* D+69 D+87 +18 April 11 Kansas 4th R+29 R+6 +23 May 25 Montana at large R+21 R+6 +16 June 20 Georgia 6th R+9 R+4 +6 June 20 South Carolina 5th R+19 R+3 +16 Nov. 7 Utah 3rd R+35 R+32 +3 Dec. 12 Alabama Senate R+29 D+2 +31 2018 March 13 Pennsylvania 18th R+21 D+0.3 +22 April 24 Arizona 8th R+25 R+5 +20 June 30 Texas 27th* R+26 R+21 +5 Aug. 7 Ohio 12th R+14 ? ? Partisan lean is the average difference between how the constituency voted and how the country voted overall in the last two presidential elections, with 2016 weighted 75 percent and 2012 weighted 25 percent. * Results are from either an all-party primary or an all-party general election, both of which include multiple candidates of the same party; vote margin is the total vote share of all Democratic candidates combined minus the total vote share of all Republican candidates combined. Sources: Daily Kos Elections, secretaries of state

Lo and behold, the special election in Ohio’s 12th has evolved into a toss-up race too, with perhaps a slight tilt toward Republicans. But this should come as no surprise: Since 2017, the margins of federal special elections have shifted leftward from their partisan leans by an average of 16 percentage points (calculated from the rightmost column in the table above). If Ohio holds an average special election on Tuesday, that would suggest a 2-point O’Connor win.

3. The polling

An O’Connor win could very well happen, but it’s worth noting that the Democrat has led in only one poll of the race. An average of the four polls taken in the final two weeks of the campaign puts the race at Balderson 47 percent, O’Connor 45 percent.

The latest polls in Ohio’s 12th District show a close race Start End Pollster Pop. O’Connor Balderson Margin 8/2 8/4 Emerson College LV 47% 46% D+1 7/26 7/31 Monmouth University* LV 45 47 R+2 7/27 7/29 Public Policy Polling^ V 44 48 R+4 7/23 7/25 GBA Strategies† LV 45 48 R+3 7/10 7/13 GBA Strategies† LV 43 48 R+5 6/13 6/16 JMC Analytics LV 35 46 R+11 6/9 6/12 GBA Strategies† LV 41 48 R+7 6/7 6/10 Monmouth University* LV 38 48 R+10 * Monmouth University polls are an average of three likely voter models: the “low turnout,” “standard midterm” and “Democratic surge” models. ^ Poll conducted for liberal group End Citizens United. † Internal poll conducted for the O’Connor campaign. V = voters; LV = likely voters

Democrats might make a few points to argue that their candidate will outperform the polls. They might point out that O’Connor has closed the gap significantly over the past couple of months. The implication there is that O’Connor will continue to surge — perhaps right into the lead — in the race’s final “poll” on election day. But as we’ve shown in the past, this concept of “momentum” in general-election polling is a myth. Democrats also might trot out early voting statistics, which appear favorable to O’Connor: As of July 26, 54 percent of early votes had been cast by Democrats compared with 31 percent by Republicans. But in Ohio, a voter “registers” for a political party by simply voting in that party’s primary election — an unreliable indicator for one’s true partisan feelings. Plus, the early vote is accounted for in polls, so we shouldn’t give it any weight above and beyond that. In fact, the decision to vote early may be correlated with other vote-deciding factors like enthusiasm, so the election day vote could look substantially different. As a result, early voting data has often led would-be predictors astray. (Remember this if and when O’Connor jumps out to a big lead in the initial returns Tuesday night.)

No, the best argument that Democrats have on their side is that polls of U.S. House races have high margins of error, and polls of special elections have margins of error that are higher still. If the polls say Balderson has a 3-point lead, then a realistic reading of their uncertainty would suggest that any outcome from O’Connor+10 to Balderson+16 is possible. This was elegantly demonstrated by Monmouth University in its last poll of the race. Monmouth modeled three possible electorates for the special election and arrived at a different outcome for each: one in which Balderson led by 5, one in which Balderson led by 1 and one in which O’Connor led by 1.

4. The political geography

If, as the polls suggest, O’Connor does fall short of Democrats’ 16-point average overperformance in special elections, demographics could be one reason why. Despite a (fading) narrative that affluent suburbia would sweep Democrats to victory in 2018, Democrats have actually overperformed the least in those types of districts in 2017-2018 special elections. By contrast, areas that swung hard for Trump in 2016 (compared with how they voted for Mitt Romney) have seen the biggest swings back to the Democratic Party.

The Ohio 12th is indeed characterized by affluent suburbia. Stretching north and east of the state capital of Columbus, the 12th District encompasses Ohio’s wealthiest county (Delaware) and well-to-do suburbs like Dublin and New Albany. It is the classic home of the country-club Republican: It has been represented in Congress by only two men since 1983: the business-friendly Tiberi and Kasich, the face of never-Trump Republicanism. The district is predominantly non-Hispanic white (86.3 percent); 39.6 percent of its population over age 25 has a bachelor’s degree or higher (compared with 30.3 percent of the U.S. as a whole); and it has a median household income of $66,774 ($11,452 higher than the national median).

But here’s the twist: Ohio’s 12th District is the rare piece of affluent suburbia that voted (slightly) more Republican in 2016 than it did in 2012. According to calculations by Daily Kos Elections, Trump carried the district 53 percent to 42 percent, and Mitt Romney carried it by 54 percent to 44 percent. That barely perceptible shift hid some serious movement beneath the surface:

Partisanship by county in Ohio’s 12th District Comparing 2012 presidential results with 2016 presidential results County 2012 Margin 2016 Margin Swing Delaware R+23 R+16 D+7 Franklin* D+3 D+19 D+16 Licking R+14 R+29 R+15 Marion* R+26 R+48 R+22 Morrow R+24 R+50 R+25 Muskingum* EVEN R+29 R+29 Richland* R+13 R+29 R+16 12th District total R+10 R+11 R+1 * Results are only for the part of the county in the 12th District. Source: Daily Kos Elections

Suburban Delaware and Franklin counties, which together are home to a majority of voters in the 12th District and therefore weigh most heavily in the district’s overall demographics, did indeed shift away from Republicans with Trump on the ticket instead of Romney. But the five remaining counties that the 12th District covers (either in part or in full) shifted toward Trump much more dramatically, canceling out the swing of the former counties. Drive east from Columbus on I-70 and you’ll reach Zanesville’s Muskingum County, which saw a margin shift of 29 points toward the GOP in 2016; north on I-71, the district reaches as far as the county seat of Richland County (which shifted 16 points rightward in 2016), the old manufacturing city of Mansfield. These counties are home to the same white working-class and rural voters who swung Ohio from Obama+3 to Trump+8. Will they snap back to Democrats as sharply as their brethren in other special elections have done? If so, it might be enough to negate any smaller-than-average leftward shift coming out of stubbornly Republican Delaware County (which hasn’t voted Democratic in a presidential election since 1916).

Ultimately, we don’t really know from where O’Connor and Balderson will draw their strength: the suburbs or the outer counties. That can make it challenging to follow the results in real time (polls close on Tuesday at 7:30 p.m. Eastern), as it won’t be obvious who is doing better than expected. To help you along, we’ve calculated county benchmarks based on two different paths to victory in the 12th District: the 2012-based path (Democrats win the outer counties, Republicans win the suburbs) or the 2016-based path (Republicans win the outer counties, Democrats win the suburbs). The numbers below represent how we would expect each county to vote if the race were exactly tied districtwide. If the counties are voting more Democratic than their benchmarks, then O’Connor is on pace to win. If the counties are voting more Republican, then Balderson should start warming up his victory speech.

County benchmarks for Ohio’s 12th District How each county might vote if the race were tied districtwide, according to two different voting patterns County 2016 Vote Share 2012-Based Benchmark 2016-Based Benchmark Franklin* 32% D+13 D+30 Delaware 27 R+13 R+5 Licking 21 R+3 R+18 Richland* 8 R+2 R+17 Muskingum* 6 D+11 R+17 Morrow 4 R+14 R+38 Marion* 1 R+15 R+37 Benchmarks are based on two different paths to victory in the 12th District: the 2012-based path (Democrats win the outer counties, Republicans win the suburbs) or the 2016-based path (Republicans win the outer counties, Democrats win the suburbs). * Benchmarks are only for the part of the county in the 12th District. Source: Daily Kos Elections

As you can see, the big difference is Franklin County, which is home to a plurality of 12th District residents and is its only true blue terrain. Under the 2016 path to victory, O’Connor needs to really run up the score there to offset losses pretty much everywhere else in the district. But the 2012 path to victory allows him to merely win Franklin comfortably while also winning Muskingum and breaking roughly even in Licking and Richland.

5. The bottom line

We’ll repeat the same thing we’ve been saying for every special election: Pay attention to the final margin, not necessarily who wins. A 1-point win for Republicans would obviously be nice for Balderson, but such a bad performance relative to the district’s partisan lean would still bode poorly for overall Republican chances in November.

Thankfully, we may be past the point where pundits have massive overreactions to special elections. Midterm season is well upon us — Election Day is 13 weeks from today — and it seems like there’s a new poll released every day to feed the nonstop narratives. Those distractions will help put the 12th District result into proper context: an interesting data point, but still only one of many.

Dhrumil Mehta contributed research.

Check out all the polls we’ve been collecting ahead of the 2018 midterms.