Of course, you can’t make an ironclad prediction about the general election based on these top-two primary results. An average error of three points on major party vote share (or six points of margin) means that most close results are still a tossup, and that there are occasionally outlying results. The error is also bit larger in open seats (four points) than in those with an incumbent (2.9 points).

But this is about as good as any data we’re going to get. The average House poll over the final three weeks of an election is off by an average margin of 6.2 points, according to FiveThirtyEight. So the primary results are a bit like getting a free round of more than 50 final House polls in early June.

And in contrast to late House polls, the direction of bias in the top-two primary is fairly predictable. There’s generally a slight Republican bias, on the order of a little more than a point, presumably because the primary electorate tends to be somewhat older and whiter than the general electorate. The exceptions to this pattern have come in years with one-sided presidential primaries, like 2016, when Democrats had a competitive presidential primary race after the Republican primary was over.

The results are good enough that you can put some stock in a surprise. In 2016, for instance, Darrell Issa’s seat was rated “Safely Republican” by the Cook Political Report heading into the primary. But he ended up claiming just 50.8 percent of the vote, to 45.5 percent for the Democrat, Doug Applegate, presaging the closest House election of the cycle. In the end, Mr. Issa won re-election with just 50.3 percent of the vote.