The presidential caucus isn't, in any formal or legally-defined way, an 'official start'; but it might as well be, in effect.
'Personal turn' is a turn (change in the course of events) that is characterized by arguments about candidates rather than policies.
If he is a 'personification' his person represents an idea. This was formerly used in elaborate compliments: 'You are generosity itself' [in fact they are just very generous, but the personification makes the compliment more telling.] As Latin words used for virtues tended to be feminine nouns, many statues and paintings personify them: charity, liberty, poverty, hope... that sort of thing
Note: 'personification' is often (perhaps as an extension of its formal use in compliments) used in a loose sense to mean 'extremely <adjective>'. But in your example the word is used in a more precise sense: somebody's person has become the symbol of a protest.
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