The emoluments clause is the most obvious example. The Russia collusion is treason, of course. And it's pretty straightforward to argue that obstruction of justice, which he is committing pretty routinely at this point, is a Constitutional violation of his duties. A slew of further violations come into play if you consider that he must follow the law in his administration of the executive - the first being a flagrant violation of the ethics law against nepotism by hiring his son in-law. Etc etc.