[1] Some of you might think that the choice of Wallace seems farfetched, but remember that this is 1969, not 2020. The Southern wing of the Democratic Party was still very powerful at that time. Knowing Humphrey’s death was imminent, it’s plausible that Wallace and his Dixiecrat allies would agree to support Humphrey in January of 1969 in exchange for the Vice Presidency, which would be vacant right after Muskie ascended to the presidency.
[2] Ask your (grand)parents:
https://en.wikipedia.org/wiki/The_Odd_Couple_(film)
[3] Based on his real-life apology, albeit ten years later. Whether Wallace was actually sincere is a matter of debate, but I would expect that this sort of deal would require him to publicly renounce his pro-segregation stance.
https://www.washingtonpost.com/wp-srv/politics/daily/sept98/wallace031795.htm
[4] Similar issues surfaced during Muskie’s OTL Presidential run. I found an article in
Jet magazine from 1972 suggesting that Muskie was avoiding the Black community during his 1972 campaign. Also, in OTL, Muskie opposed the idea of having a Black running mate, for fear that such a ticket would not be “electable”:
https://www.nytimes.com/1971/09/09/archives/muskie-rules-out-a-black-running-mate.html