The US military is NOT "growing cool" towards the F-35, it is that they are trying to lay the groundwork in the politician's minds (such as they are) that the program is still affordable, so that if Obama is elected president, and the Democrats still control both houses of Congress, there won't be an outright cancellation of the program as being "unnecessary" (the F/A-18E, and F-15/16 & small numbers of F-22 are good enough for "purely defensive purposes", and the Demos won't venture into hostile territory for any non-UN reason).
The F-35 is needed in numbers for "offensive" missions, the thought of which sends convulsions of horror through the likely budget-masters, so the services are beginning their campaign to preserve some F-35 acquisitions right now.