Remember, Churchill was a member of the hereditary aristocracy with inherited wealth, which he seems to have spent or misinvented to a great extent - that's the point of the book being reviewed here. That was a big key to power.
The lone exception being that excitable German with the Charlie Chaplin moustache...
Being in prison also accomplishes that goal.
Ideally you should be in prison for political reasons, because most other crimes may be detrimental to improving social status in the future.
And countries that put you in prison for political reasons have no overlap with countries that have comfortable prisons that encourage and nurture self-improvement, contemplation and creative pursuits.
Being jailed by your political opponents, whatever the reason, is generally unlikely to hurt your social status if you do get to power eventually, since even non-political charges can be dismissed as politically motivated.