[niteowl77]

but since when a sitting US senator can not talk to an official of another country

Senate or house, if it is a Democrat (Kennedy, Harkin, Kerry, Pelosi…) it is okay, and a Republican "maverick" (McCain, Amash..) can do it.

Nobody else can.

Mr. niteowl77

[RayChuang88]

My guess is that this Russian ambassador has spoken to many members of Congress--including Senate Minority Leader Charles Schumer and House Minority Leader Nancy Pelosi. Aren't ambassadors supposed to meet with important national politicians of the countries they're assigned to in the first place? (If I remember correctly, when Joseph P. Kennedy was US Ambassador to Great Britain, he became well-known to both Labour and Conservative leaders through many meetings.)