It is illegal to attempt to make foreign policy as a private citizen.
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Any citizen of the United States, wherever he may be, who, without authority of the United States, directly or indirectly commences or carries on any correspondence or intercourse with any foreign government or any officer or agent thereof, with intent to influence the measures or conduct of any foreign government or of any officer or agent thereof, in relation to any disputes or controversies with the United States, or to defeat the measures of the United States, shall be fined under this title or imprisoned not more than three years, or both.
I honestly don't think my or your opinion matters with regards to that.
If he tells a foreign official anything at any point in time whether it be email, phone call, twitter etc. it's official. He can't claim that he was taking a break. He can delete a tweet, but that doesn't mean that it didn't happen.
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Any citizen of the United States, wherever he may be, who, without authority of the United States, directly or indirectly commences or carries on any correspondence or intercourse with any foreign government or any officer or agent thereof, with intent to influence the measures or conduct of any foreign government or of any officer or agent thereof, in relation to any disputes or controversies with the United States, or to defeat the measures of the United States, shall be fined under this title or imprisoned not more than three years, or both.
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https://en.wikipedia.org/wiki/Logan_Act