Sometimes you can walk along and step on a stick, or a board, which happens to be in a seesaw position, sitting on a pivot point. Your foot goes down on the board, and a short time later the other end of the board flies up and hits you in the face. Our federal legal system sometimes operates that way in history.
Prof Somin says Trump's sanctuary cities EO is unconstitutional. One of the ironies of history in our federal system is the way decisions spring back to strike people. In this case a Supreme Court decision on part of Obamacare which liberals disliked may come back to support liberals. See Somin's post for the details. This is another example of how federalism works--James Madison would be happy.
Another outcome of federalism is the promotion of hypocrisy--politicians may be on one side of a federalism issue while in power, the other side when not in power.