The question is related to the genitive case usage in Eng. language.

I have found some examples where the genitive "s" has been dropped as:

1. Part of the reason was a lack of liberal positions on the Kennedy platform.
2. Do you feel the Bush Administration has done enough in response to Hurricane Katrina?

Why without "s" after Bush or Kennedy ?

Kennedy and Bush are here used as defining adjectives. Other examples:
a calculus book
a cancer specialist
an asphalt driveway
For more on defining adjectives, see http://www.fortunecity.com/bally/durrus/153/gramch21.html#2a6

There are four ways in which nouns indicate possession:
of ...
two consecutive nouns (defining adjectives)
For more on this, see http://www.fortunecity.com/bally/durrus/153/gramch17.html
ok this is fine, but how to make a difference between:

Bush administration was ... and
Kennedy's interest was ...

Is there any strict rule to or should guess a bit ?
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Some of it is guesswork or familiarity with the different usages. But I think the rule would be: try to determine if the first noun defines the second one (a brick house), or if it merely indicates possession (the Smiths' house). In some cases either will work: George Bush's administration, or the Bush administration. But the meanings are slightly different.