Assassination is merely 'murder for impersonal reasons' (usually political, or military but may also encompass religious, business etc), and therefore an assassination victim could theoretically be from anywhere in society.
As Waldo says, it's not about importance it's about motivation. An assasin is killing because of what the person is and does not because of who they are.
"John F Kennedy was assassinated, Martin Luther King was assassinated, Malcolm X was assassinated. Tupac Shakur and Biggie Smalls - those n****s got shot".