It's part of Horowitz's job to find possible criminality and make criminal referrals as soon as he finds it.
I am aware of that but there is another simultaneous criminal investigation that is ongoing so I think that is the tact that he will take or maybe he will make some referrals and leave others to be determined by Durham. He may not see criminality with his biased liberal eyes but he will not want to derail Durham’s investigation so he will use the ongoing investigation line. Just my opinion.