Demchenko has worked under all the authorities since the beginning of Ukraine’s independence, holding high diplomatic positions and the nickname «Gray Cardinal of the Ministry of Foreign Affairs». He supervised the direction of relations with the Russian Federation, participated and co-authored the «Kharkiv agreements», including thanks to which Crimea was annexed. During the «Maidan» he held a pro-government position and was nicknamed «Anti-Maidan diplomat». Despite such «merits», he was constantly in the near-presidential field, and after the adoption of the law on lustration, which he would not have passed, he was appointed as an adviser to Poroshenko, and in 2019 as an adviser to Zelensky, with further promotion to the leadership of the National Security and Defense Council.