Also, what do you do if the hate speech is posted or linked to by a notable public figure, such as the President of the United States or a member of Congress?
> hate speech is posted or linked to by a notable public figure
Here's how I would approach it. Accounts that are tied to real identities have a much higher threshold for bans -- public figure or not. Sans a credible threat of harm to specific individuals they can largely say whatever they would like, hateful or not. When pseudoanonymous accounts get flagged their choice is to attach a publicly visible identity to the account or be banned.
If you think this is easy, you don't understand the problem.
2) Because zero-tolerance tends to result in over-blocking, and they already have a problem with banning content that shouldn’t be banned.