Major news outlets such as the the Associated Press and Fox News have not yet called Pennsylvania — the state that would give Joe Biden the 270 electoral votes he needs to win the presidency — as of 10:50 pm Eastern.

Biden took the lead from President Trump in the Pennsylvania count Friday morning, and soon afterward, Vox’s election-calling partner, Decision Desk, called the state for Biden. But the other major election-calling outfits — NBC News, CBS News, NBC News, Fox News, CNN, the Associated Press, Reuters, and the New York Times — have not yet done the same.

As I wrote Friday morning, Decision Desk called Pennsylvania for Biden because its assessment of the votes that remain to be counted — how many there are, where they’re coming from, what type of votes they are, and how similar votes have broken down previously — is that the remaining votes will favor Biden strongly. Decision Desk anticipates Biden’s current lead of about 28,800 votes, a 0.43 percent margin, will expand as the count continues. (Indeed, it has already expanded significantly throughout Friday — it was at about 6,500 votes when Decision Desk called the race.)

That expectation is shared by many election wonks. FiveThirtyEight’s Nate Silver tweeted that the outcome in Pennsylvania is “obvious,” the Cook Political Report’s Dave Wasserman tweeted Friday that there’s “little reason” to think Biden’s Pennsylvania lead won’t hold up, and the New York Times’s Nate Cohn wrote that “it seems just a matter of time before the race in Pennsylvania is put out of reach” for Trump. However, none of the news outlets these analysts are working with — ABC for Silver, NBC for Wasserman, and the New York Times for Cohn — have called Pennsylvania yet.

Why not?

It’s possible that most or all of these outlets are close to calling Pennsylvania, but Biden’s lead is just a bit too small at this point for them to feel comfortable doing so. They may be waiting for Biden’s margin of 0.43 percent of the vote to rise above 0.5 percent — the threshold that would no longer mean a mandatory recount — before calling the race. The Pennsylvania vote count has been agonizingly slow, so it may just be taking a while to get there.

A broader issue here is that it would be extra-embarrassing to incorrectly call the state that decides the presidential race, so even small levels of remaining uncertainty may make the networks gun-shy. And the quick Fox News and Associated Press calls of Arizona for Biden may have made many a bit more cautious (it currently looks like Biden will keep his lead there, but Trump has regained significant ground in the count since then).

But MSNBC host Steve Kornacki laid out a more extensive case that there’s some real uncertainty remaining Friday afternoon. (We should note that Kornacki is not actually in charge of these calls — NBC’s Decision Desk is — but he gave the most detailed public explanation of this line of thinking.)

Kornacki’s argument is as follows:

• Biden’s lead is currently small — when he spoke, it sat at 14,000 votes, a mere 0.21 percent margin, though it has since doubled — and the count is not done.
• The remaining tens of thousands of mail ballots to be counted will heavily favor Biden. But there’s some uncertainty about exactly how many of them will end up being counted; some could be rejected. So it may not pad his lead by as much as some expect.
• Most importantly, Kornacki said, there are reportedly around 100,000 provisional ballots out there in Pennsylvania that add uncertainty to this whole situation.

Provisional ballots are ballots cast when there’s some question about whether someone is truly eligible to vote, or some problem with the ballot itself. Most of them have not yet been counted, and elections officials will eventually have to decide whether to accept or reject them.

The traditional assumption has been that provisional ballots tend to favor Democrats. But, Kornacki asked, what if this time they don’t, due to various technicalities associated with the partisan polarization of mail balloting? Kornacki pointed out that a few Republican-friendly places have counted their provisional ballots already, and that they favored Trump.

Note that Kornacki did not say he thinks the larger universe of 100,000 provisional ballots will favor Trump. He is just saying that he would prefer to see more of them counted to feel totally confident about what’s going on with them.

But other analysts do not think it’s at all likely that the Pennsylvania provisional ballots will give Trump back his lead, for a few reasons.

First off, provisional ballots are provisional — some of them will be counted and some won’t. Only the ones that actually count will matter, and that will be less than the overall number that were cast.

Second, Kornacki emphasized that Trump was doing well in provisional ballots in Trump-friendly counties. But as Wasserman points out, Trump’s performance in these provisional ballots was not really much different from his overall performance in these counties.

This matters because there were also many provisional ballots cast in Democratic-friendly areas — we don’t have an exact tally from every county yet, but Philadelphia, Allegheny County, and other areas where Biden has performed very well will make up a large share of the overall total. If the provisional ballot vote largely resembles the rest of the vote in these areas, then it’s Biden who will pick up votes here — a lot of them.

To even make up his current 28,800-vote deficit, Trump would need to win the overall universe of approved provisional ballots across the state handily. And remember, Biden’s lead is expected to grow as tens of thousands more mail votes in Democratic areas are counted. The more Biden’s lead grows, the better Trump would have to do in approved provisional ballots to make up the gap.

Those pushing for a quicker call think the scenario of Trump utterly dominating provisional ballots statewide is fanciful. But the rebuttal was essentially, it’s a weird year, it’s a small margin, and with so many potential ballots outstanding, it can’t hurt to wait a bit longer and get a bit more information. We will see how much longer that wait will take — but later on Friday night, as Biden’s lead expanded, Kornacki increasingly sounded like he’d seen enough.