The problem of interference in an election is a tricky one. Even if you can provide evidence it occurred you then have to decide what influence it had and what to do about it. Do you declare the election of Trump and the result of Brexit null and void and have a re-run? The American constitution is very well set about for most eventualities like assassinations and removal of Presidents for reasons of illness or illegality, but they are all predicated on the assumption there is a next-in-line to take the Present's place. They did not envision any situation where the entire line might be invalid. So who is in charge and what authority do the have while a rerun takes place?

Similarly with Brexit. Do you have another vote? If you say (as we should have done in the first place) that it is the job of Parliament to decide, won't they be heavily influenced by the now-void result?

Difficult.