>So when a city declares itself a 'sanctuary city'

...they are saying that because immigarion law is federal (as you point out) they will not assist in its enforcement.

>democrats to just bring in tens of millions of illegal immigrants

No one, except the immigrants themselves, brought the immigrants here. That's what makes one an immigrant....they immigrate.

>Why can't we just go back to having a rule of law?

This is a very apt question being asked daily of the Trump administration.