Before his death Alberic made the Romans swear to elect his son, Octavian, when Agapetus died. In 955 this promise was fulfilled and the young man became John XII. His conduct as pope was scandalous and his politics unsuccessful. In Feb. 962 he crowned the German king Otto I Holy Roman Emperor and obtained from him a confirmation and extension of the temporal powers of the papacy, the so-called Ottonian privilege (Privilegium Ottonianum). But a proviso to the Ottonian privilege gave the emperor power of ratification over papal elections.

The pope and the emperor soon quarreled. Otto had John deposed and replaced by Leo VIII (Dec. 963). When Otto's duties took him away from Rome, John again obtained control of the city and took vengeance on his foes. Leo fled (Feb. 964). John died (May) before Otto I returned to Rome, and the Romans immediately elected Benedict V. Otto had Benedict deposed and sent into exile while he restored Leo VIII (June).

[a couple paragraphs later...]
Otto III named as John XV's successor the first German pope, his 23-year-old cousin Bruno, who took the name Gregory V and immediately crowned the emperor (May 21, 996).
-- “Papacy” in ENCYCLOPEDIA BRITANNICA (1969).

[St. Helena is named in the Roman Martyrology on August 18,...;it is observed universally in the East, but on May 21, with that rather equivocal person, her son Constantine: the Byzantines refer to them as “the holy, illustrious and great emperors, crowned by God and equal with the apostles. --BUTLER'S LIVES OF THE SAINTS.

I wonder what would happen, if anything, if all Catholics could pray to Constantine as a saint.]

Maybe it just comes down to enjoying the odds of all this.