Big talk and political posturing does not equal action. "if you don't stop bothering me I'll have my dad beat up your dad" isn't the equivalent of felony assault. It is talk.
It is the explicit job of the executive to take action implementing legislative decree (laws). Many -- probably *most* -- of the laws have several vague parts that say "make it so", without any details. Frequently they're along the lines of "just do SOMETHING", giving a LOT of leeway to the actual implementation, allowing for all sorts of exemptions, delays and the ability to deal with unforeseen issues.
Whenever you see things like "refusing to uphold the law" start thinking about "unfunded mandate". Congress says "do this -- but we aren't giving you money". You need to prioritize based on resource constraints.
If 10,000 people come across the border, and I have 100 cops and limited court resources for due process where do I prioritize? Focus on the 10 year-olds looking for their mommy? Or the convicted felons and known violent offenders? They are NOT equal in the effort needed or resources consumed.
So, again, [Citation Needed]. Please point to a specific example. The ONLY one I can think of that might be a violation of law is the trade of Bergdahl for the Guantanamo inmates. Maybe.