A two-point advantage might leave the House balanced on a handful of districts. A lead of five or six points begins to overcome the Republican advantage built into the map.
At the moment, Democrats appear to be above that threshold.
Best estimates are that they have roughly a 70 to 80 percent chance of taking the House. The likeliest outcome would be a Democratic gain of perhaps 15 to 25 seats, although redistricting, candidate quality and polling error could make the majority considerably smaller.
The Senate Is a Different Country
Republicans entered the cycle with 53 seats to 47 for the Democratic caucus. Democrats need a net gain of four, which means they must first protect every seat they already hold and then win four Republican ones.
They must hold Georgia, where Jon Ossoff will face a closely divided electorate and an enormous Republican effort to defeat him. They must also hold Michigan, where an open-seat contest could be affected by the kind of primary divisions Democrats have repeatedly mistaken for philosophical enrichment.
Then the climbing begins.
North Carolina is the most plausible Republican pickup. The seat is open, the state is closely divided and the Cook Political Report has called it the Republican seat Democrats are most likely to flip.
Ohio offers another real opportunity because Sherrod Brown is not a generic Democrat. He has spent years talking about work, wages and unions in language that sounds as though he has met people who have jobs. But Ohio has moved sharply Republican. Brown can win it; he cannot be penciled in.
Alaska has become genuinely competitive. Texas could become competitive because Republicans nominated the deeply polarizing Ken Paxton. Neither is naturally Democratic territory.
Until recently, Maine was supposed to be the more dependable opportunity.
Graham Platner had defeated the Democratic establishment and built a campaign around his identity as an oyster farmer, Marine veteran and working-class insurgent. Then his candidacy disintegrated under a series of disclosures and, finally, a sexual-assault allegation that he denies.
Platner withdrew, leaving Maine Democrats to select a replacement at a party convention only months before the election. The field includes former Maine Senate president Troy Jackson, former state public-health director Nirav Shah, Secretary of State Shenna Bellows and several others.
There is something painfully human in what happens next.
Thousands of Maine voters chose Platner in a primary. Volunteers gave him their evenings. People sent him twenty or fifty dollars because they believed he might defeat Susan Collins. Now a relatively small group of party delegates must choose someone else, while those voters are asked to transfer their enthusiasm as though it were an unused airline ticket.
The replacement may turn out to be excellent.