But what about Bernie Sanders? Another new poll Tuesday - this time in Iowa - seems to fill out the picture of a 2016 runner-up who didn't impress last week and is losing ground.
The CNN poll had Sanders dropping, albeit less than Biden did. While Sanders had 18% support in late May, the latest national poll put him at 14%. He dropped to fourth place but was still in a statistical tie with Harris (17%) and Warren (15%).
Tuesday's Iowa poll, though, is worse. Sanders is again in fourth place, but this time he's not so close. And that might not even be the worst part.
Here are the top-line numbers from the Suffolk University/USA Today poll in Iowa:
Pete Buttigieg: 6%
This is Suffolk's first Iowa poll, but Sanders is well below his 16% showing in an early June Des Moines Register-CNN poll and his 22% in a CBS News-YouGov poll last month. It's also just the second time he's been in the single digits in a poll either nationally or in the early states. A Post and Courier poll of the South Carolina primary recently also put him at 9%.
But while Sanders got drubbed by Hillary Clinton in South Carolina last time around (by 47 points), he very nearly won Iowa. He lost to Clinton by just a fraction of 1%, in fact. It was his big coming-out party. Now he's languishing in the single digits there, at least according to one poll.
And the bad news in the new poll doesn't stop there. Suffolk also asked which candidate people would vote for as their second choice, and just 6% picked Sanders. You might think that many Sanders supporters from 2016 would flirt with another candidate, perhaps, and that maybe he was still their backup. But you would be wrong.
In fact, when second choices are factored in, Sanders actually drops behind Buttigieg, who is the second choice of 14% of voters (and who also out-fundraised Sanders in the last few months).
Sanders's supporters are also less likely to turn out to vote. Among those claiming to be "very" likely to caucus next year, he is again struggling to top Buttigieg:
This all comes with some important caveats. One is that Sanders's base might say it's less likely to vote simply because it's younger. And his supporters certainly wound up being motivated enough in 2016.
Another is that it's one Iowa poll. Even if it builds on the national CNN poll, this is a snapshot of a moment in time. Perhaps Sanders just had an uninspiring debate, and voters are checking out their options. There are many more debates and lots of time.
But when you're the runner-up in a presidential nominating process, you usually start the next one with some heft and a built-in base, even if you don't enter it as the outright favorite. As of right now, Sanders appears to be losing some of his base to Warren and is headed in the wrong direction overall.
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