General Discussion

Great question, it’s important to understand what premise they are operating underneath.

Near as I can tell (I’m not a lawyer) the majority of the authorization for federal intervention in blue states is the Supremacy Clause (Article VI, Clause 2) which makes federal law supreme, allowing federal agents to enforce valid federal laws nationwide, including in any state, regardless of state politics. Trump’s position is they are deployed to the individual states to enforce the Federal Immigration laws that our sanctuary states avoid.
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https://constitution.congress.gov/browse/article-6/clause-2/

Please understand I’m not taking the feds side, just explaining what I assume is their justification.
If we want to have our lawmakers approach this from a well grounded understanding so they can better resist.