Why Fox’s Call on Arizona, Which Was Right, Was Still Wrong

Through a Fox News spokesperson, Mr. Mishkin said he “misspoke on election night” when he said Fox expected Mr. Biden to win the remaining vote. If Mr. Mishkin did misspeak, there was still no indication that the Fox team expected Mr. Trump to win the remaining votes by a meaningful margin — let alone an overwhelming margin.

On air on election night, Mr. Mishkin offered two main reasons to expect Mr. Biden to fare well in the remaining vote:

“Yes, there are some outstanding votes in Arizona. Most of them are coming from Maricopa, where Biden is currently in a very strong position. And many of them are mail-in votes, where we know from our Fox News Voter Analysis that Biden has an advantage.”

On their face, these arguments weren’t outlandish. Mr. Biden won Maricopa County, which is the home of Phoenix and a majority of Arizona voters. He won the mail vote in Arizona as well.

In the end, Mr. Trump won 59 percent of the remaining vote, all but erasing Mr. Biden’s advantage.

What Fox missed

How could a group of mostly mail-in and mostly Maricopa ballots break for Mr. Trump by such a wide margin? 

The reason was foreseeable before election night.

While “mail” votes sound monolithic, there can be important differences between mail ballots counted before and after the election. That’s because Arizona counts mail ballots in roughly the order in which they are received, and different kinds of voters return their ballots at different times.

Ahead of the election, it was clear that Democrats were turning in their ballots earlier than Republicans. As a result, the mail ballots counted on election night — those received at least a few days before the election — were likely to break for Mr. Biden by a wide margin.

The flip side: The voters who received mail ballots but had not yet returned them were very Republican. If they ultimately returned their ballots, these so-called “late” mail ballots counted after the election would break heavily for Mr. Trump.

It wasn’t inevitable, of course, that Mr. Trump would win these ballots by as wide a margin as he ultimately did. It was possible that many of these Republicans would simply vote on Election Day. In the midterms last November, for instance, Republicans failed to decisively win the “late” mail vote under fairly similar circumstances.