I think he needs to do exactly what he did in Illinois and California during the Democratic Primaries, where he performed quite well among racial/ethnic minorities....
Most of his worse performances among minority populations were relatively early on in the primary season, in particular among older African-American voters in Southern states.
I suspect to some extent that was more of a factor of the popularity of the "Clinton brand", than any major issues with a lot of Bernie's policy positions, combined with a significantly higher name recognition factor for Clinton, as well as the "electable factor" that the Clinton campaign used against him early on.
One could certainly make a decent argument that Bernie struggled a bit as well with minority voters in the larger Metro areas of some Northern States as well (NYC & Philly spring to mind), but it does appear that as the primary season developed his numbers performed much better.
Obviously how any hypothetical 2020 contest would play out among any Democratic voter demographics would be dependent on how is running and what themes are accentuated by the respective candidates trying to cobble together a winning electoral coalition.
We have to talk about all areas. In NYC for example, Bernie's best numbers were among Asian Americans (even better than Whites),
same in Michigan - Look at Dearborn. Hawaii is full of Asians & Bernie won big. In Illinois, Nevada, CO, MN, the exit poll showed Bernie winning hispanics. He won the native American votes in Washington, Alaska, Oklahoma, etc. It is just that he really did poorly among the black community.
Look at Michigan, Illinois, Ohio etc - He was getting between 30-40% of the black votes while in the South he was being decimated with 10-15% of the Black votes. He improved massively with time or it is perhaps a geographical divide (more likely).
I do think he wouldn't have many of the handicaps that he had in 2016 - Socialist, Independent, Unelectable, perception of being anti-Obama, Northern White guy with no connect to Blacks etc etc.
In a divided field it will be hard for any candidate to unite the Black vote like Clinton did - Only Booker to some large extent can if he tries to run as Obama II. Biden definitely has the opportunity to unite the black vote, he is Obama's VP & almost a brother & Obama may tacitly endorse him (with many interviews). But Biden did worse than Edwards last time, so it's difficult to predict his support.
The only case where I see a Bernie/Warren losing is in a - Bernie vs Warren vs Booker/Biden with 2 people of the Bernie/Warren wing splitting the votes & 1 guy uniting the Southern black & establishment vote.
I didn't realize that Bernie performed better among Asian-Americans in NYC than "Anglos".... that's actually an interesting point that I haven't seen before, and quite fascinating to see not only the original source of the data, but what particular Asian-American demographics in the Big Apple were most receptive to the Bernie message. Looking forward to seeing your source material, since it slipped under my radar, most likely because I was slightly depressed that my "horse in the race" didn't win, and realized after the NY primary the deal was likely over, excepting some massive late shift dynamics in the race, which would effectively have required something of the equivalent of a Bernie landslide in Cali to maybe convince some super delegates to reconsider....
Sure, Dearborn makes sense, and I suspect (Although unfortunately we don't have many data points regarding Arab-American voters overall (Heavily Christian and to some extent Muslim) vs South Asian/ East Asian voters, etc) ) outside of some relatively isolated areas that Clinton significantly won the extremely complex and diffuse "Asian-American" vote by significant margins nationally.
I was looking at the "Asian-American" Democratic Primary vote primarily from a "West Coast" perspective, where if one were to examine certain precincts in the major cities of the West Coast (Seattle & Portland, as well as San Francisco), and not to mention some of the data that I pulled from other places such as Sugarland Texas (Fort Bend County), not to far from where I lived for four years, where overwhelmingly Asian-American precincts basically voted similarly to their Anglo neighbors, it appears that Clinton won among this Demographic overall (Although this is heavily confused since not only are many West Coast Asian-Americans registered independent, and ineligible to vote in the Democratic Primaries (Especially among younger voters) ).
That being said, Asian-American Working-Class and Middle Class populations are harder to identify, since this population frequently much more dispersed, within heavily Anglo or extremely ethnically diverse population centers. Still it's pretty much completely impossible for Bernie to win Oakland California, without a significant Black, Asian, and Latino level of support, especially since the data is well established that upper-income and wealthy Anglos in California, and the Bay Area in particular generally supported Clinton by Yuuuge margins.
So, to wrap back around to the original posters thread....
It is definitely clear that that Bernie's performance improved dramatically over the course of the primary season, with a combination of both greater name recognition, increased dialogue and outreach to a wide variety of ethnically diverse communities in America, as well as much greater receptiveness to the fundamental message of the campaign once it shifted outside of the initial IA/NH/SC and later Super Tuesday.
Bernie if he decides to run, just needs to keep being Bernie. Authentic, town hall Forums in local media markets, addressing the concerns and issues of Working Class America, and stay true to what the fundamental issues are in America, what needs to be done to fix it, and continuing dialogue with various communities from McDowell County West Virginia (Where he was at last week), to Detroit Michigan, Fresno California, not to mention small rural communities of family farmers in places like Minnesota, South Dakota, and Georgia....
He's not a politician.... not a man of rank and privilege, just a humble person who is old enough to get a ton a respect all around the block for speaking his mind, and nowhere close to the typical flip-flop politician that speaks outside of both sides of their mouths for political gain.
It's kind of odd in a weird way.... so many of the Trumpistas still believe that Trump is actually that way, but the reality is that Trump has yet to take one single principled position on any of his key "One Page triple spaced paragraph" key line item "core policy platforms".
Bernie will do just fine if he chooses to run in 2020 among a wide variety of Democratic voters, in fact if the current Trump nuclear meltdown continues, I would not be surprised to see a significant shift in party affiliation numbers come 2018 and then further into 2020, when what really Americans are seeking most is an honest political figure that is not a politician, who can effectively communicate and deliver a message that resonates with a large majority of Americans.
Bernie landslided heavily Asian Hawaii, some heavily Hispanic areas of Washington and California, but the most ignored thing was how he did with Native Americans. I think he did better with Native Alaskans than non Native Alaskans, even having Hillary fail the 15% viability in many areas, and his Alaska performance was damn good to begin with. And while it wasn't that kind of blowout landslide, he did well in Native American areas of eastern Oklahoma, northern Minnesota, and other places.