Both Uses

disillusion
in
Killing Kennedy
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He passes the time in their small cabin writing rants about his growing disillusionment with governmental power.†
p. 87.4 *

disillusionment = disappointment resulting from losing false belief that something is better than it is
The murders of Martin Luther King Jr. and Robert Kennedy, coupled with the drawn-out American involvement in Vietnam, led to a national sense of disillusionment that was the diametric opposite of Camelot's hope and optimism.†
p. 299.1

Definitions:

(1) (disillusion)
disappoint by removal of false belief that something is better than it is
(2) (meaning too rare to warrant focus)