Democratic Primaries

He lost both NH and Iowa - although Iowa was Harkin's state and Tsongus was from a neighboring state. He then lost the next two, before he won many southern states on the first multistate day. He did not clinch the nomination until some time in June. Of course, he was not as well known as VP Biden. Muskie won Iowa and NH in 1972. If you count Republican primaries, the description of being ahead, fading, losing funding and then recovering and winning sounds like McCain, who did win NH.

Saying that something is "unprecedented" ignores that it was not until 1972 that the current system of primaries and caucuses everywhere was in place. That means the number of years that there was an open Democratic nomination without an incumbent is only 9. 1972, 1976, 1984, 1988, 1992, 2000, 2004, 2008, 2016. Each of those years are pretty unique, if you look at how they played out. 2000 was essentially similar to having an incumbent President - even though Bradley, a very capable Senator challenged Gore. Of the remaining, 2004 likely was the fastest to converge around a nominee with Kerry only losing losing 2 states (Oklahoma, where he was about 3 percent below Edwards and Clark who essentially tied with Clark slightly ahead and SC where Edwards won. After Kerry was the defacto nominee, both Vermont and NC had favorite sons win in their elections. )

Biden's likely win - even if there were no coronovirus - would probably have been more solid - in terms of both delegates and number of states than any of previous year other than 2000 and 2004.

1972 was a mess with McGovern winning 21 states ( I had forgotten how successful Wallace was - he was second with 10 states)
1976 Jimmy Carter had 30 states including every Southern state.
1984 Gary Hart won 26 states and it came down to a multistate day in June for Monday to get enough delegates - there was some controversy near the end about superdelegates. I guess you could say this was most like 2008 - with the outcome reversed.
1988 Dukakis won 30 states in a very divided primary that stayed competive longer than this year.
1992 Another year that dragged on until June - Clinton ultimately won 37 states after NOT winning the first 5. Starting in early April, Clinton won every contest by large amounts, but it took until California voted in June to get the number of delegates.
2008 similar to 1984, except after ST Obama had the edge and never gave it up.
2016 HRC won 34 states and won over 50% of the pledged delegates in June when CA and NJ voted. She was always the heavy favorite.

So, which year looks the most like this year would likely have looked without the virus (and no unexpected BIG event for any candidate)?

Here is a link to a NYT article that was written on March 12, before anyone realized how much the country would change with Corona virus - https://www.nytimes.com/interactive/2020/03/12/us/elections/delegates-bernie-sanders-joe-biden.html To summarize because it is likely behind a paywall:
- the first chart is the prediction based on Biden doing as well as he has so far - every future state would go to Biden, some were identified as close others as big wins. They predicted he would have 50% of the pledged delegates by late April or early May.
- The next chart showed what would happen if Biden lost 12% of his popularity. He would still win the majority of delegates, but if it fell more than 12%, it would likely be a contested convention. (Note they said this would happen even if he did not win Illinois, Arizona and NY where he was then (March 12) still favored. -- Obviously, Biden is in even better shape having decisive wins in AZ and IL.)
- The next chart looked at what would happen if Sanders improved his support by 17% (and Biden stayed where he was) - That was the magnitude needed for Sanders to win a plurality of the vote. Note that simulation included solid wins in IL and AZ and a close loss in FL - none of which happened - meaning at this point he would need more than that 17% improvement.
- For Sanders to get the majority, it would require a 21 % increase - and as noted he did not do anything remotely like that in last night's states. Consider this even included a close win in FL!
I suspect that the NYT might update this, but I also think it would be beating a dead horse!

From this, it is clear that Biden would likely win all the remaining states - clinching in April when NY, DE, PA, RI and CT voted or possibly early May. This would likely be the third easiest - after Gore and Kerry, but before all the others.