Actually no. Basil's US citizenship can be revoked now if an USA citizenship file a court case but Basil can prove that he didn't commit treason because everything he did, it damaged Sri Lanka. But he gave an oath as the finance minister (if he did) that questions his allegiance to USA. But become the president and everything you do will be questioned by both countries. If USA declares war on SL at some point the we will automatically lose the president. So being a dual citizen and the president of country at the same time is not that simple as you may think it is.