I do not believe when Barr brought up investigating spying against the Trump campaign he was talking about the Feds. This is the Trump administration talking.
I believe they are going after their two most hated rivals. Hillary Clinton and Barack Obama. I suspect they are going to try and come up with a case of the Clinton campaign spying on Trump and lay the blame on Hillary and even drag Barack Obama into the conspiracy and try to see if they can’t bring charges against Hillary and other top members of her campaign.