In 19th-century psychology, the idée fixe was understood as a close relative of monomania and obsessive-compulsion, often accompanied by symptoms of hysteria such as amnesia or anesthesia, the inability to feel.
Idées fixes developed secondary to some sort of trauma or dislocation, and could even take the form of reenacting a past action that was once appropriate but now, in the new out-of-context context, had became bizarre. The idée fixe, as such, was a neurotic symptom. "The elements in it are persistence in or out of relation to its apperception (or context) and invariability in a new context or under a new stimulus," according to the chapter on "Névroses et Idées Fixes" in Oxford University Press's Mind, Volume 9, which in 1900 described what was originally a French concept for an English-speaking audience.
I bring this up because of President Obama's harsh words for congressional Republicans during his news conference Friday, which garnered such headlines as "Obama torches GOP", "Obama Slams GOP" and so on. But what has grabbed headline writers most is the phrase "ideological fixation." "President Obama: GOP health care pushback an 'ideological fixation'" trumpeted Politico.