Just moving 9 Counties between states could have resulted in both Mitt Romney and Hillary Clinton winning the electoral college in 2012 and 2016, respectively:
Philadelphia, PA --> NJ
Mahoning, OH --> PA
Trumbull, OH --> PA
Lucas, OH --> MI
Lake, IL --> WI
Leon, FL --> GA
Baldwin, AL --> FL
Imperial, CA --> AZ
San Diego, CA --> AZ