Were there any red flags that indicated the race would be closer than polling suggested?

[Progressive Pessimist]

-The reporting coming out about gargantuan Trump support among Cubans and Venezuelans in Miami-Dade.

-The Biden campaign's choice to unilaterally disarm when it came to on-the-ground organizing as much as the GOP were. It was the proper thing to do for Biden to appear as the serious adult when it came to the pandemic but it was not worth it since the GOP didn't give a f*** in turn and continued doing what they were.

-Polling indicating that the economy was still Trump's biggest advantage...somehow.

-Voter registration data.

-And really just in general prematurely deciding that polls were accurate again because they were better in 2018 and that Americans somehow became more sane after four years.

Thankfully none of that was enough to truly overcome a Biden victory.

I didn't include the Selzer poll because even though it was disturbingly accurate in regards to the races in Iowa, I really don't think it actually said much about the nation as a whole and even its neighboring states.

[Wormless Gourd]

- lot of people put stock into early/mail data by party registration; one guy modeled the expected R share by county vs what had been reported so far in Florida, and Miami-Dade/SE FL had Republicans voting at much higher rates then anticipated while the D advantage in smaller urban counties wasn't nearly as great
- 2016 presidential - 2018 statewide election swings foreshadowed some Trump improvements in 2020, like 2016 presidential vs 2018 governors in TX, Miami-Dade getting 10 points redder, etc.
- there was a theory(by Shor?) that 2016 was as off as it was due to white liberals that are very political active responded too much to polling vs other demographics. this proved to be less of a problem in the '18 midterms as that demographic was who ended up voting. the problem was sure to return in 2020 and polls can't account for demographics that don't trust pollsters, think it's bad taste to discuss politics with strangers or can't be reached online
- reelection years create unique coalitions, where the party in power is more of a tangible voting option for people who aren't ideological but may vote uniformly(like in big, international cities or non-English speaking communities). trump was always gonna have a high floor.

[Skill and Chance]

According to the book “Lucky”, the Biden campaign internal polls showed a much closer race. That’s why they sent both Biden and Obama to Michigan those last few days. They also knew they were never competitive in Texas, Ohio, and Iowa.

The week before the election, they gave up on Florida. They did not expect to carry it by Halloween. To their credit, they did predict winning Georgia.

At the end of the day, the only state they were wrong about were North Carolina but they expected it to be a toss up anyway

I do not believe that the Biden campaign secretly had accurate polls.  They might have had marginally better information than the public data, but you still have to explain why both campaigns were behaving like Biden had a clear lead in NC for the last ~2 months and, more egregiously, the serious Biden effort in Ohio, including campaigning in Cleveland(!) the day before the election.

[Shaula🏳️‍⚧️]

2) Biden's surprise comeback on Super Tuesday as the least "progressive" and the most "populist" candidate

Most POPULIST???
what about BERNIE

[ملكة كرينجيتوك]

2) Biden's surprise comeback on Super Tuesday as the least "progressive" and the most "populist" candidate

Most POPULIST???
what about BERNIE

Re: "Why is Sanders underperforming?" (Feb 2020)

Because he's simultaneously become more tied to the post-Obama/Trump-era Democratic Party and pulled a lot of cargo cult bourgeois socialists into or around his campaign. Meanwhile, other candidates have adopted some of his policy proposals and made a joke out of them.

Also, the fact that he's approaching 80 (he literally had a heart attack!) is not going to go away as a concern.

Different and arguably less appealing coalition than in 2016 (see also PR's post) + less support from Independents + no longer really perceived as a "fresh face", certainly less so than in 2016 + underwhelming base turnout + still perceived as an "agent of change" but less so than four years ago + less support from anti-establishment and rural voters + running against stronger opponents than Clinton ("not Hillary" isn’t really an option this time), etc.

My theory is that voters on the left wing of the party are already supporting Sanders (or maybe Warren), meaning that most of the late deciders are more centrist, conservative, or non-ideological, and a lot of these voters are turned off by Sanders's ideology. Exit polls showed that about half of New Hampshire Democratic primary voters thought that Sanders is too far left.