Endorsing Hillary or Bernie will be a total non-issue in 2020

[I spent the winter writing songs about getting better]

Just stating a fact. There has literally never been a Presidential primary in history where who a candidate endorsed last election was even a minor issue, much less the decisive one. In fact it seems to have no real correlation with who a candidate's support comes from. Note Rick Santorum endorsing Romney in 2008 or Hillary going from winning every county in WV in 2008 to losing every county to Sanders in 2016.

Why? Voters have short memories. Ask a typical person on the street now who Mitt Romney is, maybe half will be able to give the answer of the 2012 Republican nominee and another quarter or so will have some vague recollection of his name but not know who he was exactly. Ask people in Iowa who Marco Rubio is, most probably won't know. Once the new primary rolls around there's a bunch of issues people care about that define that primary, and whether a candidate supported who they voted for last time isn't too high on the list. The fact that we think it is is evidence of the bubble we live in which leads to the sort of belief every single Sanders voter is a die-hard Bernie Bro who wants to back Our Revolution to a hilt and every single Hillary voter is a deep into the establishment insider...but obviously that is not true. For about 80% of the voters of both candidates, you probably won't even find significant differences in ideology or views.

That's not to say of course that a candidate who runs on the same sort of issues can attract the same supporters, but it's a bit absurd to say that someone like Elizabeth Warren, Sherrod Brown or Kristen Gillibrand could never attract Bernie supporters if they did run such a campaign simply because of their 2016 endorsement, furthermore there's the absurdity of thinking that someone as baggage filled as Tulsi Gabbard is basically immune to all of that simply because of her endorsement and nothing else. If Bernie runs again, yeah he'll probably get a lot of the same type of supporters but not all, he could lose WV to a more conservative but not as bagged filled candidate as Hillary Clinton for example. But if he doesn't, who his supporters go to is simply not a question we know the answer to. In 2012 if you gave a list of 2016 Republican candidates and asked who would inherit most of Ron Paul's supporters, most would've said Rand Paul. Obvious right? ...well look what happened.

It's all about the issues and the campaigns they run, not some press release from four years ago.

[Vosem]

Now is a good time to point out that Hillary and Bernie have roughly equivalent, >80% favorability ratings among Democrats in most 2017 polling. The vast majority of Hillary supporters like Bernie, the vast majority of Bernie supporters like Hillary, and vice versa. Even if endorsements were something that voters remember*, no candidates would really be meaningfully hurt by the fact that they endorsed Hillary or Bernie in 2016.

*Endorsements can backfire if they are of someone who was later embroiled in scandal or were a cross-party endorsement. But these are by definition very rare.

[Mr. Morden]

I think many folks inflate the importance of endorsements because they don't know the candidates that well, and don't have much else to go on.  Similar to how people here seem to put way too much importance on the candidates' home states in assessing what voters they'll appeal to.  It's because home states is something that we know right now.  Who a candidate endorsed in 2016 is also something that we know right now.

What we don't know as well, though we have some big hints, is what kind of platform they'll run on, how they'll do in debates, how much money they'll raise, etc.  Those things are going to be more important than factors like who they endorsed in past primaries or whether they were elected in New York or Minnesota.