I found this helpful. The people who are being targeted in these initial raids have had more than a few chances to attempt to stay in the USA legally. They have chosen not to do so.
The Acting ICE Director, Matt Albence, explains what these illegal immigrants have done wrong and why they are being deported according to the laws created by Congress.
The Declined Detainer Report he explains is going to be very interesting as it starts coming out regularly. Residents of areas where the politicians are not cooperating with enforcing the law will know exactly what their elected officials are up to.