Biden’s numbers are OK in Iowa, but not great. Some 31 percent of Democrats say they have a very or strongly favorable view of him, which is essentially tied with Sanders for fourth place in the field. By comparison, 46 percent of Iowa Democrats have a strongly favorable view of Warren. (And remember, these polls are a couple of months old — she’s gained ground in most national and early-state polls since then.) Meanwhile, 40 percent also have a strongly favorable view of Harris and Pete Buttigieg.

Whenever we see a divergence between Iowa polls and national polls, the question is whether it has something to do with Iowa’s demographics or, rather, the fact that the campaign is more active in Iowa than it is nationally. If the differences are demographic in nature, then Biden might not have as much to worry about — the Democrats who turn out to caucus in Iowa are white and liberal, whereas he overperforms among nonwhite and moderate Democrats, who make up bigger parts of the electorate in states such as South Carolina and most of the Super Tuesday states. Alternatively, if Biden’s numbers are middling in Iowa because voters don’t like him as much upon prolonged exposure to him, that could mean it’s more of a canary in the coal mine, and that voters in other states will tire of Biden once they begin paying more attention to the campaign…

But getting back to Biden: Even if his issues in Iowa are mostly linked to demographics, the state could still be a major concern for him. That’s because Iowa can affect the result of every state that votes after it. These effects seem to have dampened in recent election cycles. (Just ask Ted Cruz or Mike Huckabee — or, for that matter, Barack Obama — how much winning Iowa helped them in New Hampshire.) Nonetheless, to the extent that some of Biden’s support is predicated on electability, some of it could erode if voters see him take a big loss.