So this law will be as effective as all of trumps current executive orders - not at all... This is purely a political move with not practical implications except maybe to piss off trump.
In this case Washington already does not allocate funds or encourage officers to do immigration enforcement (nor should any state really). Whats really happening here is a lot of political chest beating without any positive impact and possible negative consequences for local citizens. I want to call this out for what it is, this is Inslee and other politicians taking pot shots at Trump for personal gain. The laws aren't really changing Washington police dont do immigration enforcement anyway and have always been strongly discouraged from doing it. There are no consequences for Inslee here for taunting the Trump bear, but I could foresee future consequences for federal funds allocation for the state and its citizens. I could for example foresee increased immigration enforcement efforts in Wa State as a result of Inslees political chest beating. Ofcourse the people paying the price will be the small peons and not Inslee himself who will use that action to further his political clout.