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

It’s not a comfortable margin for Democrats, given how close these races appear. Republicans wouldn’t need much good fortune in races that were quite close.

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 aren’t many polls in these races; some haven’t been polled at all. If, hypothetically, Democrats won three or four out of the 26 races characterized as “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, Republicans led in those races by a six-point margin over eight polls taken over the last 10 days. But Democrats did narrowly lead in one of those races, Virginia’s Fifth District. And there are many more races that we won’t poll at all. It’s hard to say how many of these races the Democrats can realistically win.

The second argument is that the race is likelier to break toward the Democrats at the end, presumably because undecided voters will break for previously unknown Democratic challengers against well-known Republican incumbents.

Obviously, polls don’t predict how voters will move as 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 undecided voters are 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 as well.