I haven't seen this week's episode (7 & 8), but why did the senator do what Rossum wanted him to do? When we last saw him at the house with Echo, I thought that he had free will.
The key there (in my opinion) is the last conversation that Echo and the senator had ...
I'm paraphrasing because I don't recall the exact quote, but it was something like ...
(spoiler block in case anyone hasn't seen it yet)
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The Sen is standing over his dead wife's body.
Echo says she wasn't his wife, really, and he isn't thinking clear from all the mess they did to his head.
The Sen says he doesn't know if he can face what he just did.
Echo says that "they" (the DC dollhouse) are here, and that he can come with her and accept his free will and make his own future, or he can go with them and they'll make him forget this happened but lose all free will.
...
So, I presume that he went with them, lost his free will, had his mind tinkered and reprogrammed, and truly believes what it is that he told the committee (since those are the memories they planted in him)
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Having said all that, I have not yet seen the most recent episode either, so some new information may have come up that counters what I just said.. But the above is my understanding as I was watching that episode/scene in question.