Hillary Clinton ran as the adult in the room–the uncharismatic workhorse who could get things done–in both the 2008 and the 2016 primaries. It worked in 2016, mostly because the majority of primary voters viewed Bernie Sanders as being out of the mainstream of the Democratic Party. It failed in 2008, because there were no significant substantive differences between Clinton and Obama, and the latter was a far more attractive personality.
If Biden runs, he will be assuming the Clinton political persona in 2020. There are, however, three important differences. First, notwithstanding the recent media frenzy, he has far less baggage than Clinton. Second, he knows he’s running against Donald Trump, and can use that to his advantage. Third, and this works against him, times have changed, and left-wing millennials bent on socialism, the GND, and PC nirvana are going to be out for his blood.
Is 2008 or 2016 the more relevant precedent? I honestly don’t know; it depends on whether the average Democratic primary voter is a young activist or someone more like me. We’ll see.