In addition to the term scapegoat already mentioned above, some alternative terms that are in common use in the USA are fall guy and patsy.
The term lightning rod is frequently used in contexts where, as mgkrebs suggested, a largely innocent person, or one having only a secondary connection to some controversial issue, willingly or unwillingly takes the hit or the blame as the repercussions of a debacle unfold or expand.
Lightning rod is largely restricted to situations where the attention resulting from a poor policy choice or other bad decision needs to be deflected or diverted; it would not normally be used in more straightforward situations involving culpable behaviour. For instance, if Jonathan helped himself to his mother's home-made biscuits but blamed his little brother Billy for the act, Billy could perhaps be described as Jonathan's scapegoat or patsy; but this simple situation does not encompass the kinds of politically expedient machinations implied by lightning rod.