I am all for pursuing this as far as it will go and that is why I call for a grand jury instead of, or perhaps in parallel with, a congressional investigation.
I suggested the possibility of a parallel congressional investigation because it does offer publicity value and the main idea, since Obama is out of office, is to exploit the situation for the 2018 election and that will be hard to do working on leaks from a special prosecutor rather than from the drama of televised congressional hearings.
The problem with congressional hearings as we all know is the grandstanding by Republicans who will not work as a United team resulting in fiascoes. Moreover, the Republican leadership is likely to back off from pursuing very important pieces of the puzzle claiming that they are interfering with the criminal investigation. Finally, the congressional investigation can taint the criminal investigation and the issue of whether to offer congressional immunity in exchange for testimony has to be balanced against the desire to pursue the criminal case.
All of these things are matters to be balanced and there is no clear answer, especially in advance and especially when we do not know much of the facts that are presumably in possession of Trump
