We believe that the government shouldn't be able to go into your home without telling you, and that it shouldn't be able to get records about what books you've read, your medical records and other private records without any individual suspicion.
The provisions that are a problem are those that minimize judicial scrutiny of searches and surveillance and that increase government secrecy,
It's rather damning to their current view that they didn't need legislation. Clearly the lawyers at the Justice Department, or some of them, felt that legislation was needed to allow the government to do what it was doing.
But they do have the power to enforce federal criminal laws. So if you make unlawful presence a crime, they'll be able to enforce civil immigration law. They could charge immigrants or just transfer them to DHS, who could deport them.
It expands the jurisdiction that the Secret Service has over its ability to put in place these exclusion zones.