Nixon vs. Reagan landslide

[Kaine for Senate '18]

Nixon's worst Southern state was Kentucky, where he got 63% of the vote.  Reagan's best Southern state was Florida, where he got 65% of the vote.  No candidate of either Party will get Nixon's numbers in the South for a very long time.

[Kaine for Senate '18]

Was Nixon's strength in the South due to even stronger support among Southern whites or did he get a large share of the black vote?

It has to be both, given the numbers he got.  70% in SC, 75% in GA, 72% in FL, 72% in AL, and 78% in MS all indicate extremely high levels of white support, while at the same time needing to get a large amount of black support.  Nixon won several black belt counties, while getting 33% in Macon, AL (nobody has gotten 20% since then), winning Orleans Parish, etc.  Nixon probably represents the acme for post-LBJ Republicans among black voters.

[Kaine for Senate '18]

Nixon probably did better with blacks than Reagan did, but black turnout was far higher in 1984 than in 1972. Just look at the total votes cast in the black belt counties and this will become obvious.

I should point out, regarding turnout, that Nixon received more raw votes in Macon, AL than any other Republican has since then; likewise in several other black belt counties.