Why should congress be involved at this point when a special counsel has already been appointed?
Different purposes and different goals.
The purpose of the special counsel's investigation is to determine whether or not there was criminal wrongdoing and, if necessary, to indict and prosecute those who the investigation finds have committed crimes. That investigation is limited in scope to the criminal law implications of Russian meddling in our elections.
The purpose of the various congressional investigations is to answer a litany of other questions including whether or not a foreign nation sanctioned actions against our country, whether and to what extent America's national security was compromised, how such damage could have been avoided, and what steps can be taken to prevent such things from happening again.
