By midday Wednesday, we will likely know who won the Alabama Senate race to fill the seat vacated by Attorney General Jeff Sessions. We may not, mind you; polling in the race shows a range of outcomes from Democrat Doug Jones winning by 10 points to Republican Roy Moore winning by nine. For good measure, a Monmouth University poll released on Monday had the race as a tie, so this could end up as one of those races that is litigated for weeks to come. Or someone could win by a mile. We’ll see, I guess.

That we don’t know what will happen means that we don’t know which long chain of dominoes ending next November is going to get tipped. One of those chains of dominoes ends with the Republicans continuing to hold the Senate after next year’s midterm elections. The other, winding its way to a Democratically controlled Senate, begins with a Doug Jones win. There are other routes to that outcome, but without a Jones win, it’s much trickier.

As of right now, with Luther Strange having been appointed to hold Sessions’s seat, the Senate looks like this: The Democratic caucus includes 48 members, once you add in the independents (Sens. Bernie Sanders (I-Vt.) and Angus King (R-Maine)) who join the party. The Republicans hold 52 seats.

There are two options after the Alabama race, as follows.

The Democrats are within one seat of a split Senate if Jones wins. If Moore wins, status quo.

But now let’s layer in what’s expected to happen next year. Cook Political Report evaluates each of the 34 seats that are up, ranking them as solid for one party or the other, likely to be won by one of the parties, leaning toward a party or toss-ups. The Democrats have a much less friendly map, with 23 seats in play to the Republicans’ nine — plus both of the independents.

About half of the seats held by either party are solid for them. About half aren’t, as below.

We can assume that each party will hold its solid seats. In that case, we go into 2018 with one of the following two scenarios.

At this point, it’s important to note another way in which the Democrats are at a disadvantage: Many of the seats they need to retain are held by Democrats in states that Donald Trump won in 2016. One Republican toss-up seat — that of Sen. Dean Heller (R-Nev.) — is in a state Hillary Clinton won.

You can already see how the Republicans hold an advantage. If Moore wins, they are one seat away from 50, everything else aside. That plus the tie-breaking vote of Vice President Pence means that the party will continue to be able to pass legislation if it holds its caucus together. (A big if, it’s worth pointing out.) Pick up one of the Democratic seats or one of their own toss-ups, and the Republicans are there.

But let’s continue. Assume that the political winds that are blowing right now continue to blow with the same strength in the same direction next year, and the Democrats hold all of their leaning and likely seats (10, plus King’s in Maine).

With seven toss-up seats, the Democrats need six (if Jones wins) or all seven (if Moore does) in order to take control.

Here are all of the toss-up seats — with the results in those states in 2016.

  • Corker (R-Tenn.). Trump won by 26 points.
  • Donnelly (D-Ind.). Trump won by 19 points.
  • Flake (R-Ariz.). Trump won by 3.5 points.
  • Franken (D-Minn.). Clinton won by 1.5 points.
  • Heller (R-Nev.). Clinton won by 2.4 points.
  • Manchin (D-W.Va.). Trump won by 42 points.
  • McCaskill (D-Mo.). Trump won by 19 points.

Those are some pretty grim numbers for the Democrats. They don’t tell the whole story, mind you, since, for example, Manchin will certainly do much, much better than did Clinton. But still, it’s an uphill climb.

In the interest of playing this out, let’s assume that the Democrats hold all their seats. That gives us this.

Let’s throw in Heller’s seat, too, and assume that the Republicans hold the other two.

In that case, we have a 50-50 split, meaning a lot of trips to the hill for Pence to break ties. If, that is, Jones wins in Alabama today. If he doesn’t, the Republicans hold 51 seats.

If the Democrats take two of three Republican toss-ups and win Alabama and win every other contested seat next year — Democratic majority! Take out any one of those conditions, though, and no dice.

Part of the problem for the Democrats is that, in wave elections (as 2018 may turn out to be), once-safe seats suddenly become less safe, allowing the party enjoying the wave to pick them off. The calculus above, though, assumes that there are only five Republican seats that could be shifted from solidly Republican to in-play.

Those are:

  • Barrasso (R-Wyo.). Trump won by 46 points.
  • Cruz (R-Tex.). Trump won by 9 points.
  • Fischer (R-Neb.). Trump won by 25 points.
  • Hatch (R-Utah). Trump won by 18 points.
  • Wicker (R-Miss.). Trump won by 18 points.

Are Democrats going to pick up a seat in Texas? In Wyoming? At this point, it seems very unlikely.

But, then, the Democrats possibly picking up a seat in Alabama once seemed very unlikely, too.