At the time you were elected you were an American citizen. Then you renounced it and became a Russian citizen. Does the Constitution insist you renounce the presidency? I'm sure if it did he would ignore it and his legal beagles would ignore it (arf arf arf) so it would matter not one way or the other what the Constitution says about anything. He already ignores it.
He would then DEMAND BY EXECUTIVE ORDER that all of you renounce your citizenship too and convert to Russian. You would learn the language and there'd be a deadline beyond which you either spoke Rissoam fluently or you would be banned from the country and shipped to a cornfield in a far off land.
The former USA would be a Russian satellite. Mar a Lago would be it's capital of course. Another acquisition done this time from inside no war needed.
Your future looks very bright. Vodka Borscht Caviar and Nyet! How better than that can it get?