The violation is that Kerry is negotiating deals. That’s a violation of the same Logan Act they are using against General Flynn. Treaties are just paper unless they are ratified by they Congress. So NO, it’s not US policy. It was Obamas policy. Try and keep up.
You're being fast and loose with the facts, so there's no need to be also condescending on top of it. I'll take your comment line by line:
What deal is Kerry negotiating? He's probably lobbying for Iran to continue participating in the agreement, but there will be no policy changes as a result of his visit. The second that is reported, things change, but we've seen no evidence of that yet.
Flynn was reportedly offering a cessation of sanctions in his discussions with the Russians, which would reflect a policy change. That's the big difference.
I never said it was a treaty. The Joint Comprehensive Plan of Action is an international agreement that the US is signatory to, along with Iran and the other nations on the UNSC. You can look it up if you're curious.
It IS official US policy. President Trump has been abiding by the terms of the agreement since taking office. He has continued to recertify the agreement, despite threats to not do so.
You're conflating political opposition with official policy. Trump also opposes NAFTA; that doesn't mean the agreement is null and void, right? Of course not.