If sanctuary cities feel they have a moral obligation to take in immigrants and even those here illegally, then they should use the law to their advantage instead of ignoring it. Federal law requires persons here illegally to be fined a minimum of $50; it does not mandate jail time or deportation.
So sanctuary cities could fine all the illegals in their city limits, pay the fines for them, be in full compliance with federal law, and retain their sanctuary status.
For most cities the financial cost would be a drop in the bucket of their annual budgets. These cities could then say to the Trump administration: “The law requires us to fine illegals; OK, they’ve been fined. Next issue.”