Aaron Blake: “The divergence in Iowa polls highlights a challenge for observers early in the 2020 election: While we have an abundance of national polls, early-state polls have been few and far between, and that makes it incredibly difficult to draw conclusions about whose organization and message are appealing to the voters who matter most. It’s not clear yet whether we have a true and accurate picture of the race, even as it stands now.”

“The pace of early 2020 polls is significantly slower in Iowa and in New Hampshire than it was four years ago. The poll Wednesday was just the second live-caller poll released in Iowa since the beginning of August, compared with six over the same period in 2015. In New Hampshire, there have been just two over the same span in 2019, compared with four in 2015.”

“If you expand the universe to all quality polls and stretch it further back in the race, the pattern holds. There have been just seven quality polls, including automated and online surveys, in Iowa since the start of May, compared with 14 over the same period in 2015.”

David Byler: “But we’re not completely in the dark about who is going to be the Democratic nominee. National primary polls taken at this point in the process don’t have a great track record of picking the eventual winner. But one of the candidates in the top three or four in the national polls often does become the nominee. And while true polling longshots — those polling at zero percent or close to it — do still have some chance of winning, the historical record doesn’t provide much reason for optimism.”

Perry Bacon: “In the runup to the 2016 presidential election, this same question came up, and FiveThirtyEight analyzed general election polls from 1944 to 2012 that tested the eventual nominees and were conducted in the last two months of the year before the election (so for 2012, that would be November and December of 2011). On average, these polls missed the final result by 11 percentage points.”

“The last presidential election featured one of the more accurate sets of early polls for this point in the cycle: Hillary Clinton led Donald Trump 46.2 percent to 41.2 percent in an average of all polls conducted in November and December 2015, missing the eventual national popular vote margin by about 3 points. (The actual result was Clinton 48.0 percent, Trump 46.0 percent.)”

Nathaniel Rakich: “There are already a lot of things that a smart poll-watcher has to account for when comparing surveys. Were they done by the same pollster? Did they query the same type of population (likely voters, registered voters, all adults)? To this list, the volatile 2020 Democratic primary field has added one more: Do they ask about the same candidates?”

“With upwards of 20 candidates and potential candidates, pollsters are forced to make editorial decisions about whom to ask about. And with new candidates still popping up out of nowhere, the field is enough in flux that it looks different every month.”

Politico: “The logjam of nearly two dozen declared or likely Democratic presidential candidates is overwhelming public pollsters trying to measure the 2020 primary. New surveys are cramming up to 23 Democrats into their questionnaires after the [DNC] set a low, 1 percent polling threshold to gain admittance into the party’s first primary debates.”

“The miles-long list of candidates has created an unusual set of methodological challenges for pollsters already battling declining engagement with their surveys. But pollsters say the criteria also put them in a no-win situation: A pollster’s decision about whether to include a candidate or not could be a make-or-break choice for that campaign, especially the lesser-known and first-time White House hopefuls hoping to make the debate stage.”

“Warning: exit polls are like online dating profiles. Things may not be as they appear. And they may break your heart.”

— 2016 Clinton campaign manager Robby Mook, on Twitter.

For those looking for the latest midterm election polls, there are almost no good quality polls of the most competitive races in these final days.

Nate Silver: “The fundraising numbers are so good for Democrats — and so bad for Republicans — that it’s hard to know quite what to make of them. From a modeling standpoint, we’re extrapolating from years in which fundraising was relatively even, or from when one party had a modest edge, into an environment where Democrats suddenly have a 2-1 advantage in fundraising in competitive races. Moreover, this edge comes despite the fact that a large number of these competitive races feature Republican incumbents (incumbents usually have an easier time raising money than challengers) and that most of them are in red terrain.”

“If Democrats beat their projections on Nov. 6 — say, they win 63 House seats, equalling the number that Republicans won in 2010, an unlikely-but-not-impossible scenario — we may look back on these fundraising numbers as the canary in the coal mine.”

“That data, plus Democrats’ very strong performances in special elections, could look like tangible signs of a Democratic turnout surge that pollsters and pundits perhaps won’t have paid enough attention to. Right now, in fact, the polls are not showing a Democratic turnout advantage.”