Democrats Have Numbers on Their Side in Battle for the House. Republicans Have the Map.

Dozens of House races in the midterms, according to New York Times Upshot / Siena College polls, making it easy to envision a Democratic blowout or a district-by-district battle for control that lasts for weeks of counting beyond the election.

The difference between the two outcomes will depend on whether or not Democratic Republic of the Republic. The Democratic gains in predominantly white, well-educated suburbs have stretched the Republican majority exceedingly thin. Fighting against this partisan polarization, which could allow Republican incumbents to narrowly hold on to the circumscribed by the president.

The uncertainty is not just about hedging. It's a reflection of the sheer number of highly competitive districts, and the limited data available about each one. There are usually only one or two polls of the most competitive breeds. It is a very different information environment of a presidential election, when there are dozens of polls of a handful of highly competitive states.

The polls can be wrong, of course, as they were in crucial states in 2016. But in a presidential race, we at least know what the polls say about Pennsylvania or Florida. This time, we do not know what the polls say in most districts, and the polls could be wrong even if we did not know.

But taken in the aggregate, the dozens of Times / Siena polls a picture of a still certain race.

The Democrats show the least of the 23 districts they need for control, since they seem plainly favored in 16 districts held by the Republicans, while the Republicans seem favored in two seats held by the Democrats.

Those 16 districts are rated as "Democratic lean" by the Cook Political Report, and the recent Times / Siena polls of those districts show Democrats ahead by an average of seven points. They are an interesting mix of districts, but they are often more often than not, and they are predominantly white, well-educated suburban districts that voted for Hillary Clinton.

After that, things get murky fast. The Democrats have put many districts into play. There are 29 races rated "tossup" by the Cook Political Report and 26 considered "lean Republican." The Democrats would need to win a mother of those 55 districts to take control.

The Democrats are considered clear favorites to win control because of the number of opportunities they have to do so. They are competitive in so many races because they have recruited many strong candidates, and they are constantly growing in size and money.

All the conditions for a wave election remain in place. It's a midterm year, when the president's party status struggles; the president 's approval rating is beneath 50 percent; and the Democrats hold a high-single-digit lead on the US Congressional Bullet, which asks them whether they vote for Democrats or Republicans for the House.

But this year, such an election does not guarantee anything like the 63 seats in the previous wave of the election. The Democrats do not have much to do with, because of partisan gerrymandering and the tendency for Democrats to win by lopsided margins in urban areas. Alone, it's enough to give the Republicans a chance to survive that would give the Democrats a huge majority.

Indeed, the map remains the Democrats' big challenge. Most of the districts that are in play lean Republican in presidential elections, and it is not obvious that the Democrats actually lead in a lot of them.

The results in the race have been reduced to 12 in the past 12 individual districts, and in the past 12 individual districts polls are fairly noisy, but the group is clear: The tossups are really close.

The Democrats need to win only about one-third of the tossups to win the House. So if the polls we've taken to this point were exactly right (they're not, and no one should expect polls to be), Democrats would take control by a modest margin. Maybe they'd pick up 27 to 30 seats.

It would be a wave, on paper, given the limited opportunities that Democrats have on favorable ground. But it would not necessarily feel like a wave. The race could not be called for days, California and Washington count late mail ballots.

It's not a comfortable margin for Democrats, given how close these races appear. Republicans would not need much good luck

The view that the Democrats are more overwhelming favorites depends on one of two interpretations of the data.

One argument is that Democrats are likely to win at least a handful of "lean Republican" races. There are not many polls in these races; some have not been polled at all. If, hypothetically, Democrats won three or more of the 26 races characterized by "lean Republican" by the Cook Political Report, it would make the Republican path to victory exceedingly narrow.

In our polling, the "lean republican" races live up to their label: On average, we have a six-point margin over eight polls taken over the last 10 days. Goal Democrats did narrowly lead in one of those races, Virginia's Fifth District. And there are many more races that we will not poll at all. It is hard to say how many of these races the Democrats can realistically win.

The second argument is that the race is likely to be at the democrats at the end, presumably because of the unwillingness of the voters.

Obviously, polls do not predict how voters will move we approach the election. But there's nothing about our polling that would rule out this theory. Many Republican incumbents are stuck around 45 percent, and in several districts the predominantly young, nonwhite and democratic. And Democratic challengers are spending millions in the closing weeks to increase their name recognition. The national political environment, which still favors the Democrats, would give them a bit of wind at their backs.

If there's any truth to this theory, let's go to the Democrats. They would also break through a number of "lean" Republican districts where Democrats are in striking distance. The "blue wave" would not just materialize – it would be like a blue wave, too.

But there's still a big force on the G.O.P. side: the Republican-lean of the battleground. If Republicans can polarize the electorate along the lines of recent presidential elections, they will lock the Democrats into that disadvantageous map.

Over the last month, the race has been trended somewhat in that direction. Republicans have pulled ahead in red-state Senate contests. If it holds, it is a big shift from the last year of special election results, when Democrats routinely fared extremely well in Republican-held areas. It would be more like last year's Virginia general election, when results were highly correlated with the presidential race.

Fully 18 of the 29 tossup districts voted for President Trump in 2016, and so did 24 of the 26 "lean Republican" races. So it would be more likely to help the Republicans run the table in the "Republican lean" contests and stay in the game in the tossups.

Alone, a more polarized electorate would not be enough for the Republicans to win. Too many Republicans have retired. Too many gerrymanders have been weakened by the time since 2014. But it would keep them in striking distance. It would be a late election night, and they would not need too many more lucky breaks to hold on.