This should only embolden efforts for parts of western Washington to break away and become part of Idaho. If one state were to succeed in changing its borders in this way it would open the floodgates for a national realignment of state borders that would Balkanize the leftists areas of many states. Next domino would be Minnesota where the western half of the state would be joining the Dakotas
I assume you meant Eastern WA but it's a moot point. For a portion of any state to join another state they need "permission" from their state's legislature. Oregon has been talking about it for 50 years.In the past few years a handful of OR counties have voted to do this but they still need the OR legislature to approve. Would be the same in WA state.