This awesome interactive tool from data scientist and mathematician Kevin Wilson lets you reassign counties from one state to any other state. As you can see above, even just a few minor changes could radically alter the balance of power in a given state, and consequently the Electoral College, too. Wilson took the presidential election results and population statistics for each county and has his widget automatically add or subtract them if you move them between states so that you can calculate the Electoral College outcome, while the map lines also show the changes at both the statewide or county level.
In this hypothetical, I moved just three counties between neighboring states. I gave Lake County, Illinois, to Wisconsin, along with Lucas County, Ohio, to Michigan, and finally Camden County, New Jersey, to Pennsylvania. Those three changes would have caused all three states that gained counties to flip from voting for Donald Trump to supporting Hillary Clinton, and in the process she would have instead won an Electoral College majority of 279 to 259 (Wilson’s tool doesn’t account for Maine and Nebraska splitting their votes by congressional district).
This exercise helps show just how absurd and arbitrary today’s Electoral College biases are, and how relatively modest changes in historical boundaries could have sparked large consequences today. You aren’t just limited to modest changes either, since you could see how crazy moves like giving Los Angeles County, California, to Texas would flip the Lone Star State, or how Trump would have carried Virginia if West Virginia had never seceded. Check out Wilson’s tool to see for yourself.