https://thinkprogress.org/john-kerry-ma ... f1571b061/
"Rubio was one of the 47 Republican senators who signed a letter sent to Iran’s leadership in 2015, while Obama’s White House was negotiating the nuclear deal, that said any agreement between the two nations without their approval could be undone by the next president “with the stroke of a pen.” Rubio has not commented on whether his 46 Republican colleagues or he could also be subjected to potential FARA or Logan Act charges."
Maybe you should have a more clear set of rules on what is and is not allowed. If an ex-US president bumps into a UK prime minister, are they allowed to have a chat about global affairs?
There was a key (and one suspects deliberate) untruth in that article, which alleged that "Rubio was one of the 47 Republican senators who signed a letter sent to Iran’s leadership in 2015." In fact, they didn't send anything to anyone. It was an open letter on Senate letterhead addressed to the "Leaders of the Islamic Republic of Iran."
https://data.bloomberglp.com/assets/sit ... eaders.pdf
Kerry clearly violated the Logan Act. Rubio equally clearly did not.
They do have a clear set of rules