Obsession
ob.ses.sion \a:b-'sesh-*n, *b-\ \-'sesh-n*l, -*n-*l\ \-e-\ n 1: a persistent disturbing preoccupation with an often unreasonable idea or feeling 2: an emotion or idea causing such a preoccupation - ob.ses.sion.al aj
Fanaticism
fa.nat.i.cism \f*-'nat-*-.siz-*m\ n : fanatic outlook or behavior
Better still:
Fanatic
fa.nat.ic \f*-'nat-ik\ \-i-k*l\ \-i-k(*-)le-\ \-k*l-n*s\ aj [L fanaticus inspired by a deity, frenzied, fr. fanum temple] : marked by excessive enthusiasm and intense uncritical devotion - fanatic n
Two completely different words, to wit:
Radical Islamic fanatics are obsessed with violence.
On the other hand:
Rick is obsessed with GWB, of whom he is a fanatical critic.
Note: These examples are associated only in the use of fanatic and obsession. No other association is expressed or intended.