But, on balance, the new survey data out this week have been some of Sanders’ best, even amid recent public tiffs with Elizabeth Warren, Hillary Clinton and Biden — and also as Sanders is trapped in Washington during President Donald Trump’s impeachment trial.

Here are three more things we’ve learned from this week’s polls:

Don’t count out Biden

The CNN and WBUR polls mentioned above provide ample evidence of Bernie-mentum. But they aren’t the only polls out this week, and the others are far less conclusive about Sanders’ position.

Nationally, there was a Monmouth University poll showing Biden leading Sanders by 7 points among Democratic primary voters, 30 percent to 23 percent. The two men were well clear of the third-place candidate, Warren, who was at 14 percent.

Even in New Hampshire, it’s not clear that Sanders — who won the state by more than 22 percentage points in 2016 — is a strong frontrunner. A Suffolk University/Boston Globe poll released Tuesday showed Sanders (16 percent) just a tick above Biden (15 percent), Buttigieg (12 percent) and Warren (10 percent).

The two New Hampshire polls aren’t directly comparable in one important way, though. The Suffolk poll showed nearly a quarter of Democratic primary voters, 24 percent, are undecided. But the WBUR survey, which included so-called “leaners” — voters who initially say they are undecided but, when asked, say they are leaning toward one candidate — pegged the “undecided” number at just 5 percent.

Sanders' strength with young voters could be decisive

That the oldest candidate for the Democratic nomination appeals to younger voters isn’t new: Sanders routinely won young voters in the 2016 primary over Hillary Clinton. But the latest polls show how Sanders’ base could power him to the top of this crowded, splintered 2020 field.

Age has become one of the defining cleavages of the 2020 Democratic race. In the CNN/SSRS national poll — in which Sanders has a slim, 3-point lead over Biden overall — Sanders is the top choice of 39 percent of Democrats under the age of 45. That’s 21 points ahead of the next closest Democrat, Warren, another septuagenarian who appeals to younger voters.

On the other side of the ledger, Sanders is the first choice of only 16 percent of Democrats 45 and older. His strength halves again, to 8 percent, among those 65 and older. Biden, meanwhile, wins 33 percent of 45-and-older Democrats, and 37 percent of the 65-plus set.

It’s a similar story in New Hampshire. A new WBUR-FM/MassINC Polling Group survey released on Thursday showed Sanders at 29 percent overall, well clear of the second-place candidate, Pete Buttigieg.

Sanders is the first choice of 37 percent of voters ages 18 to 44, compared with just 24 percent of those 45 and older. That 24 percent is still good enough for a slim lead over Biden (19 percent) and Buttigieg (16 percent) among older voters in New Hampshire.

We’re still (mostly) flying blind in Iowa

Despite the trickle of new data this week, there’s been relatively little out of Iowa — with only a week-and-a-half to go until the caucuses. And what’s more, the polling that has come out there is mostly a jumble.

There have been only three publicly released polls conducted since the start of the year, and it’s already Jan. 23. Skyrocketing survey costs and shrinking media budgets are likely to blame for the dearth of polling so close to the Feb. 3 vote.

The respected Des Moines Register/CNN/Mediacom poll, which showed Sanders narrowly ahead of the field, began its last survey three weeks ago, on Jan. 2. Since that poll, only two others have been released — and one was a survey conducted by a Democratic pollster, David Binder, who typically conducts polls for private clients. (Binder worked for Kamala Harris’ campaign before the California senator dropped out of the race.)

Whether Sanders is ahead (as in the Register/CNN/Mediacom poll), or Biden is leading (as in the other two surveys), the top four candidates have been bunched together. The latest RealClearPolitics average — which is based on only those three surveys, as of late Thursday — shows Biden, Sanders, Warren and Buttigieg all clustered in a narrow, 5-percentage-point band, well ahead of the next-closest Democratic contenders.

The relationship between precaucus polling and eventual results in Iowa is already looser because of the complex caucus process, including the “realignment” of voters who start the caucus night undecided or initially back a “nonviable” candidate before choosing another contender with their second choice. But the lack of new polling introduces even more volatility into a competitive race.

Ann Selzer, who conducts the Des Moines Register/CNN/Mediacom poll, acknowledged earlier this week that there are fewer public polls than usual, but she noted that the campaigns likely know more about the state of play than the public and the media.

“We have almost two dozen campaigns in the state, so who knows what is happening with those?” she said.

There will be more polling between now and Feb. 3 — including one more poll from Selzer’s firm on Feb. 1. CNN is planning to build an entire program around the poll’s release on the Saturday night before the caucuses.