Sanders might lose too, but Biden is definitely going to lose.
Why do you think that?
Because he was basically the only candidate with many of the same problems as Trump - a neoliberal who can't complete a coherent thought and is creepy with women. Young people are not going to come out and vote for Joe Biden, I promise. Nominating Joe Biden could have decades-long effects on political participation and engagement IMO. Young people can only be told to stay in their lane by the people who got us into this mess so many times before they throw their hands up and stop participating.
You can argue whether that's right or wrong, but the turnout suppression that'll happen with the Biden selection is nearly guaranteed to result in a loss. Among the whole pool of Dem candidates, Biden is the absolute worst choice.
Is Joe Biden in 2020 a better candidate than Hillary Clinton in 2016 on paper? I don't think he is. Mentally he is going downhill at incredible speed right before our eyes - he makes no sense, misspeaks every sentence, etc. Trump is going to demolish him in the debates. That's not to say that he's going to spell out his vision better or beat Biden on policy specifics, obviously, but he's going to roast him like a bully in the middle school lunch room and that's what "winning the debate" looks like in America these days.
I feel almost exactly the opposite. I'd say Bernie and Trump are far more similar, symptoms of the same disease. Both harness the same frustration and grievance-seeking and cast themselves as anti-establishment. Both have simplistic, pie-in-the-sky solutions that more or less can't work.
Biden, to me is a placeholder candidate. Bernie would be far more dangerous long term.
As far as electability, I think we've seen how Democrats respond to Biden vs. Bernie over the last week. Biden hits all the demographics that will matter in the places that matter. He's pretty much a lock in PA, and has a puncher's chance in Florida.
Sanders and Trump are "symptoms of the same disease" in that they are both populists speaking to a major shift in the system here away from multi-national corp funded neoliberalism, which is IMO needed - that style of governance has resulted in massive wealth and income inequality everywhere it's been tried, including here, and it is getting worse. That's about where the similarities end. One of them is a total clown who doesn't listen to anyone and every action he takes is an effort at self enrichment - that is, he obviously never intended on governing for "the people" as he pretended, his populism is a fraud - and the other is very serious and has real progressive bonafides (even if you think he's TOO progressive). "He's not really a Democrat!" is my favorite criticism of Sanders - they're right, he's not; while the Democrats were still arguing for school segregation and banning gay people from getting married he was against those things. At some point having had the "right" opinion (to me) is more important than having been part of the Democratic party.
We've seen how Democrats in certain states respond to Biden vs. Bernie, and how the Democratic establishment - an organization that it's pretty hard to come up with good reasons to respect at this point - responds to them for sure. We've seen how they respond in swing-y states like Colorado (big for Sanders), fucking fucking fucking iowa (big for Sanders), Maine (close but went to Biden, with Warren still in the race), Minnesota (big for Biden), Nevada (big for Sanders), New Hampshire (big for Sanders). At the end of the day Biden running up big delegate counts in states like South Carolina (+15% for Trump in 2016), Alabama (+28% for Trump in 2016), Tennessee (+26% for Trump in 2016) doesn't mean much to me in terms of electability, and I think it's generally kind of a silly way to choose your candidate. Those three states, none of which either of them has a snowball's chance in hell to win, account for a +73 delegate count for Biden in a contest currently separated by 78 delegates. For comparison, the 6 swing states I listed combined account for a +28 delegates for Sanders in a race he's losing by 78 delegates.
As I said, I think it's fair to make the argument that Bernie Sanders is too far left to win a general election (although there is also a TON of propaganda about him - there are people in this thread talking about a 'communist revolution'). But I know Biden is going to lose, 100%. His support isn't going to go -up- as more people hear him talk in 2020. He's a disaster. I wish we had a rational "moderate" candidate but we picked the worst possible one.
At the end of the day it's going to be a hard sell to young Americans to say, "as long as we get rid of Trump, the man, we can get back to the normalcy that brought us to this point by electing an octogenarian who touches women and can't speak in complete sentences" and have them get out and vote.