I think it depends. The two main definitions I'm seeing for "assassination" are either: any intentional murder (so basically any murder is an assassination), or specifically any politically motivated murder (so a jilted lover killing the president wouldn't be an assassination, but killing your local HOA president could be).
People seem to consistently refer to John Hinckley’s shooting of President Reagan as an “assassination attempt” despite the fact that Hinckley’s motive was a delusional belief that this would impress Jodie Foster. And we still don’t know the exact motive of the JFK assassination, though everyone has their theories.