It means that the rumour is that he didn’t just make antiamerican video tapes while in captivity, but he completely broke down, told them everything he knew, and helped them. Just a rumour. And not one that was allowed to be vocalized during the campaign.
I am disposed to believe that given his behavior state side, I am not going to judge beyond accessing that he is compromised! By that I mean, I am not making a moral judgment, but a strategic judgment! Why not moral - because maybe, and even probably I would have done the same thing given the same circumstance - but strategically that means that he can not, and should not be trusted, given his irrational behavior!