He has every right to say anything he wants to say in regards to this election. This is America. Last I looked he has not suggested anyone resort to violence. If I'm wrong I'm sure you can show me why I'm wrong.
He is not in a talk show anymore, he is the POTUS, he should act responsibly at least on this occasion. Making fraud accusations, talking about stealing the election from him, and not providing any evidence, don't you think that attitude may lead to violence in the street from his supporters?
A few weeks ago he said to an extremist group to "be ready". He has been playing out this story for weeks in anticipation of defeat, blaming others has been his constant attitude towards lack of success.