A lot of people confuse the moment for the person because it's hard to take a longer historical perspective on things. The Democratic Party needed someone to challenge Hillary Clinton that wasn't Lincoln Chaffee (actual person who ran for the nomination!) or Jim "You can't ask my opponent anything because I threw a grenade at him and he's dead now" Webb. The frustrations of the Obama Administration, despite its successes, left a whole lot of people in search of more radical solutions to problems. 2016 was always bound to be a change election because that's just how US politics go. Hillary Clinton had the unenviable task of running on Obama's legacy without BEING Barack Obama. And in 2016, something like 54% of the country thought we were on the wrong track. Enter Bernie Sanders.
Bernie capitalized on a lot of the frustrations with Obama and the longer-term legacy of Bill Clinton's time in office (revisionist history being what it is). He took a lot of the anti-banking energy forward and co-opted a whole lot of movements (people act like Bernie came up with 15 dollars an hour all on his own...he didn't) into the mainstream. The result of the primary was the most progressive Democratic platform ever that made bolder claims on things like college tuition and minimum wage than either of Obama's platforms. Given the percentage of people who felt we were on the wrong track, it's not hard to understand why there was a repudiation of the battles and compromises that defined the Obama era. It's also a little nonsensical to pretend that single-payer healthcare sprung fully formed from the head of Bernie Sanders when it's been the inevitable endpoint of liberal politics since, like, Medicare (which is literally just single-payer for a certain segment of the population).
Bernie didn't spend nearly enough time or energy cultivating that support or those relationships. The polling numbers bear out exactly how hard he lost in communities of color. And black women, for decades, have been the single biggest pillar of support for Democratic politicians.
Bernie's fundamental problem is that he's an old white guy from a breathtakingly white state (Vermont) who views everything through a Marxist lens of "if we fix class problems race problems will sort themselves out." To his way of thinking, EVERYTHING is a problem created by capitalism that can be solved by Democratic Socialism. I will never claim to speak for communities of color, but from my conversations with them they're deeply skeptical of people who haven't been allies for a very long time. They still have iconic members of their communities like Jim Clyburn and John Lewis, and those voices matter. Despite her husband's record on welfare reform and criminal justice (the latter bill was supported by African-American communities at staggeringly high levels despite its legacy now), Hillary Clinton had the support of these communities and Bernie didn't spend nearly enough time or energy cultivating that support or those relationships. The polling numbers bear out exactly how hard he lost in communities of color. And black women, for decades, have been the single biggest pillar of support for Democratic politicians.
Sanders capitalized on a lot of anti-Hillary sentiment, emerging populist anti-free trade sentiment (which was and is dumb), frustrations with the divided government and limited gains of the Obama administration, and the desire to shake things up in DC. He was a good and useful candidate who saw his window of opportunity too late and came too close to the nomination to accept the reality that he only had one shot at this thing and he blew it. Politics are fickle things and leaders don't create movements so much as movements create leaders. Sure, we have re-treads win elections because they have the resources to run again and again and again and again. But by and large if you miss the moment, it's over.
Since 2016, Sanders has tried - but mostly failed - with outreach to black communities. His best shot at winning the nomination is hoping that his hard partisan support (who are hyperpartisan in their support, as his fundraising numbers demonstrate) is enough to allow him to win a plurality of voters while the POC vote (which is not institutional) splits among the likes of Harris and Booker and Biden (if he runs). It seems unlikely - especially in the wake of people who believe (rightly or wrongly) that Sanders cost Clinton the election - that he's going to improve past 15% among African-American voters (and that's charitable). He's already come out of the gate making the argument that only he can win over the white rural Trump voters that Democrats need to take back the White House. It's a specious argument at best for the general election, but it's a tone deaf argument in the primary that casts aside the voters who will be most critical to winning.
It's hard to say how much Sanders influenced the shape of modern liberal policies and how much of them were an inevitable reaction to the problems of the ACA (seriously, Obama signed a piece of legislation with critical flaws because he knew once those flaws were exposed we'd be forced to craft a public option, which is what he wanted originally and was torpedoed by turncoat Joe Lieberman), the slow growth out of 2008, the lack of accountability for big banks, fill in your pet issue here. The Fight for 15 was well underway before Bernie Sanders announced. Teacher strikes have picked up steam nationwide with no one to lead them (I eagerly await whoever invariably takes credit for that). If Sanders had read the tea leaves better, he very well could have won the 2016 primary. But it's a circular argument to say "see? everyone embraced my positions; ergo I must be the President." If anything that demonstrates that his policies will be implemented with or without him and allows us to look at the merits of the candidates.
Especially in the wake of 2018, when we elected more women to Congress and more diverse people than ever, when we elected the likes of Sharice Davids (whom Sanders backed a white guy against in the primary, lol), Rashida Tlaib, Ilhan Omar, Katie Hill, Ayanna Pressley, and made national stars out of Stacey Abrams and Andrew Gillum...any straight white guy that enters the race and says "we shouldn't be judged on gender or race" feels especially...like they're not reading the room (and yes, this logic would apply to Beto or Biden if they enter).
Every person has a right to enter the race. Sanders' entry is less misguided than others (hi Tulsi Gabbard). But the moment passed him by and he's too stubborn to admit it. The path to the nomination for him is a cynical one that hopes that the pillars of Democratic support fracture among other candidates and he can drive a small constituency (mostly young white men) to a large enough plurality to win. Because he ultimately thinks the only way to beat Trump is to pander to the same white male voters with a different vision of how to ease their anxiety with a rapidly changing cultural landscape. I've never seen that path being successful because it's not the state of the Democratic Party that I want to believe in. It's not how we won 2018 and it's not how we should try and win 2020.
I haven't decided who I'm voting for in the primary yet, but I can tell you I will work my ass off to make sure that Sanders gets nowhere near the party's nomination.