If you love election polls, Sunday was a banner day. The Washington Post-ABC News, Fox News and NBC News/-Wall Street Journal all released national primary polls. They are remarkably similar, meaning they are all accurate … or they aren’t.

Former vice president Joe Biden leads in all three (with a low of 27 and a high of 31 percent), ahead of Sen. Elizabeth Warren (D-Mass.), who draws 21 to 23 percent, by 4 to 10 points. (The Post-ABC and NBC-Wall Street Journal polls are virtually identical.) Sen. Bernie Sanders (I-Vt.) is third in all three polls with 17 to 19 percent of the vote. South Bend, Ind., Mayor Pete Buttigieg comes in fourth in all the polls, with 6 to 9 percent of the vote.

Sen. Kamala D. Harris (D-Calif.) picks up the final qualifying poll for the December debate with 4 percent from the NBC-Wall Street Journal poll, while Sen. Amy Klobuchar (D-Minn.) gets her third qualifying poll thanks to a 5 percent showing in the same poll. By contrast Rep. Tulsi Gabbard (D-Hawaii) did not get at least 3 percent in any poll, leaving her still one poll short of making the November debate.

We can detect some general patterns from this rush of polling data. Keep in mind these are national polls in a presidential primary race, and we are three months before anyone casts a vote in Iowa.

First, the percentage of undecided voters or voters willing to change their mind is very high (53 percent in The Post-ABC poll). For voters who have not spent the summer obsessing over primary coverage, they may be seriously assessing the candidates for the first time.

Second, Warren has moved steadily up in the polls from the single digits to second place. However, with Sanders maintaining a hold on a large segment of progressive voters, African American voters still strongly supporting Biden and the very real possibility that her Medicare-for-all proposal will scare off moderates, it is not clear how high a ceiling she has. Maybe her Medicare-for-all plan will win over some of Sanders’s voters, but frankly, his typical voters (younger, male, not college-educated) have stayed with him and may not see the appeal in Warren that many older, female and college-educated voters might.

One warning sign for Warren from The Post-ABC poll: “On honesty, Biden and Sanders are roughly even at 26 percent and 27 percent, respectively, while 16 percent say Warren is most honest.”

Third, despite harsh press, unsubstantiated attacks on him and his son from the White House, and less-than-stellar debate performances, Biden has held steady. Moreover, more of his voters say they are disinclined to support other candidates than other voters. Given that the other top two challengers have gone far left (e.g., Medicare-for-all), Biden is also cleaning up among moderate and conservative Democrats who make up a substantial portion of the primary electorate.

Biden retains his electability argument. A majority of primary voters think he is the most electable (42 percent in The Post-ABC poll compared with the high teens for others), and in head-to-head match-ups against President Trump, Biden is the strongest Democrat. That is critical in a primary competition in which Democrats continue to say electability is more important than agreement on issues. A flashing red light for Trump: In the NBC-Wall Street Journal poll, 46 percent say they will definitely vote against him, and only 34 percent say will definitely vote for him.

Finally, Buttigieg, like Warren, has shown significant growth since the spring. He has established himself as a solid fourth in national polls. His best chance for a breakthrough, however, clearly rests in Iowa, where he delivered a strong speech before a mass audience at the Liberty and Justice dinner on Friday and has a well-organized and enthusiastic team on the ground. In the RealClearPolitics averages, he runs second in Iowa.

In sum, we have three top candidates who seems to have particular groups of voters in their corner. Biden may benefit from being the only moderate among the three, but the test for him and the others is whether they can extend their appeal to voters supporting other candidates or with voters yet to make up their mind. The temptation is to double-down on what they do best (e.g., release a mammoth Medicare-for-all plan), but that is not necessarily a smart long-range strategy. At some point, you have to stop writing off parts of the Democratic primary electorate (as Warren seemed to do in telling Biden he was running in the wrong primary because he didn’t back Medicare-for-all) and unite the party.

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