I've been reading 1920: The Year of the Six Presidents by David Pietrusza. Although somewhat popularized and a bit sensationalized in spots, it's an interesting read, furnishing several reasonable PoDs; e.g.:
* Charles Evans Hughes was approached (through an intermediary) by Henry Cabot Lodge with the concept of accepting the 1920 GOP nomination. Hughes declined since his daughter had very recently died (of tuberculosis). Suppose his daughter had not died and was in so-so but stable health?
* The notoriously ill-tempered Hiram Johnson was the second spot on Harding's ticket, which he declined vehemently and somewhat profanely. Suppose Johnson had a dose of humility and accepted?
* Early in the balloting, Harding was no better than a mild favorite son candidate. At that point, four key delegates in Ohio were on the edge of switching their votes to Leonard Wood. What happens if they made the switch?
* Charles Evans Hughes was approached (through an intermediary) by Henry Cabot Lodge with the concept of accepting the 1920 GOP nomination. Hughes declined since his daughter had very recently died (of tuberculosis). Suppose his daughter had not died and was in so-so but stable health?
* The notoriously ill-tempered Hiram Johnson was the second spot on Harding's ticket, which he declined vehemently and somewhat profanely. Suppose Johnson had a dose of humility and accepted?
* Early in the balloting, Harding was no better than a mild favorite son candidate. At that point, four key delegates in Ohio were on the edge of switching their votes to Leonard Wood. What happens if they made the switch?