Which solution? With Hitler the only choice was capitulation or war. Marginalizing him as a madman made little difference. Is it different with this gentleman?
If he starts exterminating people and committing acts of genocide, I'd agree that his mental state would not be an issue. However, there may exist some room at this point for tit for tat regarding peace agreements and the stopping of nuclear proliferation. If you just write him or any other leader off as a madman who will not listen to reason, you limit the possibilities to finding a peaceful solution.