The link between Sanders and Warren supporters isn't as widespread as some may think. There was a poll that came out a few days ago that showed that Sanders supporters are more likely to consider Warren but not vise versa. https://www.msn.com/en-us/news/video/elizabeth-warren-is-second-choice-for-bernie-sanders-supporters-but-not-the-other-way-around/vi-AAF8tIv

I tend to think of Biden's lead being due to him being an establishment candidate, and the establishment is good at getting their voters to line up around one person, while grassroots candidates tend to have more split votes because it's based on which voters fell in love with which candidate. The grassroots fall in love, the establishment falls in line. That's why Hillary had no viable moderate contenders in 2016. Martin O'Malley, Jim Webb, and Lincoln Chafee never stood a chance because they were competing for voters that were already behind the Clinton machine. Tons of voters don't really put much thought into it either, and such candidates tend to line up behind whoever is the frontrunner. Hence why once Biden reaches certain tipping points in the polls, like losing the lead in early state polls, or the national polls, or not coming first in a primary, his momentum will stall and he'll fade, once the people who just line up behind the frontrunner are forced to think about their choice.

I think you're making too many assumptions and a lot of things would have to fall in line for that too happen. Both Warren and Harris are not up for re election in 2020 so there's nothing they can lose if they continue their campaigns. It's likely they'll stay in the race for the majority of the actual primary elections. Buttigieg on the other hand is up for reelection in 2020 and the current issues with his police department might force him to drop and actually focus on that election.

I'd consider people saying they'd vote for you to be "actual support". Yeah they're probably voting for him because they've gotten to know him and trust him but that's still support.

I'd argue it's a bit of both. Sure, Sanders and Warren are splitting the progressive votes, but Biden still has the advantage of being the most recent Vice President under Obama. Mainstream Democrats (I refuse to call them moderates) did vote for Obama and know him well, and I don't think that's gonna change much.

Warren and Harris also get much votes from persons who want to see a strong female President. This is a field where neither Biden nor Sanders can compete. Hence why in the CBS poll Harris is much favored by Warren voters, but all the males are down a peg.

All this makes Harris the pragmatic choice right now: As a women, she gets the female votes, and has a twofer for being part of a minority, too. She neither too progressive nor too conservative to piss off either side of the spectrum. The bad news is that only a few are considering her for their first choice, and I doubt that that's gonna change much.

Pretty much this.

However, the times, they are-a-changing. You can clearly see that the democrats as a whole are moving more to the left, in part to counterbalance the move to the right of the republican party. This makes the establishment a lot weaker than they were just a couple years ago. Millennials and Gen Zs in particular tend to be much more on the left side of the spectrum than previous generations, and as their numbers swell, they are pushing the party to their left side of things.

In other words, time is against the establishment candidates. The more young voters are coming to age, the more the progressives will gain in power.

I've actually heard on multiple occasions that Gen Z is shaping up to be a very conservative and libertarian generation. I've even heard they're becoming the most conservative generation since the 50s. 

It makes sense, as these things tend to go in cycles. And every generation tends to rebel against the previous, and us Millenials are a highly highly puritanical generation that's very friendly with the idea of Authoritarianism and censorship, so we're extremely susceptible to being rebelled against by the youth. And how do you rebel against neoliberalism, mainstream Authoritarian left? Conservatism and libertarianism. In the same way Millenials and Gen X rebelled against the conservative and Authoritarian boomers, Gen Z is now beginning to rebel against our puritanical culture of PC, safe spaces, and censorhsip. 

Aaaah, that's very interesting! I didn't realize that he was positing it as a choice between UBI and other programs of social uplift. Well that makes me less keen on the idea.

Still, I have to say that, being dependent on food stamps at present, a $12,000/year income floor, added to my current income, would be enough to lift me above the poverty line for the first time in my life, so I still find it kind of an appealing idea intrinsically.

He never really talks about it in that way for debates, but I think the reason he has libertarians in this coalition he talks about is because when he talks with anyone with those leanings (like Dave Rubin) he starts to talk about how UBI will replace other social programs. At which point we've gotten rid of programs designed to help those in need and replaced it with something that gives people money regardless of their situation, a very libertarian outcome. 

I understand what you mean, no other candidate is talking about an immediate solution to your situation. It's possible Yang is just letting who he talks to color how he presents his ideas and he doesn't actually plan for this to get rid of other social programs, but I still worry. Silly thing to worry about since Yang has no shot at winning, but I think the overall idea of replacing social programs with something like a UBI could persist beyond his campaign. 

I've noticed that his supporters are mostly poorer people, and the way that he talks about being non-ideological also makes sense in that connection because the fact is that most poorer people aren't very ideological. They're very practical people. He's proposing a simple idea that people like me instinctively know would help us. I think that's the source of what appeal he has. His problem for me is that he's got nothing else on offer in addition, or at least nothing else that he ever talks about anyway. After two debates, he's still just the UBI guy at the end of the day.

Biden needs less than one third of the votes of other candidates in the primaries to get well above 50%, and second-choice polls show this is more than a conservative estimate. I think he has this in the bag.... specially since he's bound to get about half the delegates already with states having a 1% threshold for it.

As for folks dreaming about vast guaranteed income networks and minimum wages almost doubling, what about joining the civilizatory process with simple measures adopted in a large number of countries, such as trade union strengthening, linking minimum wage to GDP and inflation growth, or unemployment benefits that last as long as a person needs?

Edit @DarthMetalliCube - about generation Z, this was commonly talked about a few years ago, but more recent research show they are as liberal or more than generation Y. The discrepancy could be due to the fact that generation Z is reaching college age and leaving the shadow of their parental education ( conservatives have more children than liberals, but tend to "lose" more of them in adulthood).

I'm calling the race for Biden. It's clear to me at this point that that's what's going to happen. I'm not sure what'll happen in the general election, but I'm pretty sure about how the Democratic primary contest will shake out.

Specifically, this is going to wind up as a contest between Joe Biden (representing the neoliberal and conservative factions) and Bernie Sanders (representing the progressives). There was a brief moment after the first debate round wherein that shape of the race appeared to be changing, but it keeps snapping back to this specific form.

To illustrate what I mean, let's compare the Real Clear Politics polling average of the top four best-polling candidates just before the first round of debates in June and the RCP polling averages of those same candidates now, immediately after the second round of debates in late July:

Before Any Debates

Biden: 32.1%
Sanders: 16.6%
Warren: 12.4%
Harris: 7%

Now

Biden: 32.2%
Sanders: 16.5%
Warren: 14%
Harris: 10.3%

As you can see, in the long run there's basically been no movement. As you can also see, the recent round of debates (at least according to the two post-debate polls that are now out) had no impact for either Elizabeth Warren, Bernie Sanders, Cory Booker, Andrew Yang, or Tulsi Gabbard, the ostensible winners according to the press, and neither did it cost Biden any support. (Biden was also averaging exactly 32.2% just before this latest round of debates, so his average doesn't appear to have changed at all as a result so far.)

What's more, the debates will mean progressively less going forward, as viewership invariably declines with each successive debate. The first one is the one that always matters the most by far. If that didn't change the contours of the race fundamentally (and, as we can see, it didn't), then probably nothing can.

NOW, let's add up the votes of the factions to see which one will likely emerge victorious:

Liberals (Biden + Harris) = 42.5%
Progressives (Sanders + Warren) = 30.5%

That's pretty much the same as Hillary Clinton's 12 to 14% overall margin of victory over Bernie Sanders in the 2016 Democratic nominating contest.

@DarthMetalliCube spoke of generational differences, and I'd like to remark on that as it pertains to this contest. What we see overall is that older people writ large (Democratic-oriented voters over 65, I mean) and younger people writ large (Democratic-oriented voters under 30, and more especially under 25) have made up their minds: older voters are determined to support Joe Biden and younger voters are determined to support Bernie Sanders. My generation, Generation X as we're known, in contrast, is proving, as has been assessed of us throughout our lives, comparatively disloyal hard-sells; the least doggedly tied to one candidate, and not generally aligned with either Biden or Sanders.

I think it's worth pointing out here, in this connection, that my generation, and especially the women, has also been the principal anti-Trump resistance movement demographic; the people most likely to attend most of those major protests that you've seen frequently since Trump took office. They've done surveys and analysis of the demography of these demonstrators and found their median age to be 49 and that about 70% of participants are female (whereas the Democratic Party, in comparison, is 59% female, so even relative to Democratic Party membership, the resistance movement has been a predominantly female phenomenon). The plurality of those voters prefer either Elizabeth Warren or Kamala Harris (myself included). My point is that, if the contest winds up being between Biden and Sanders, like it's almost certain to be, then to be honest I fear that that might be a bit of a turn-off for some people (especially women) of my generation (including me), who, I remind everyone, are factually the leaders of the anti-Trump resistance; the people most passionately opposed to this president and what he stands for. I worry about this becoming a dispiriting contest for Gen Xers who want a fresher candidate, and preferably a woman. People don't often talk about my generation in connection to elections because it's a smaller one, but...I'm just saying that it might not be a wise idea to flatly ignore what we want, considering that we're the (albeit unacknowledged) ideological vanguard opposing the current president and his agenda; the main source of that energy.