Very interesting question! The reason we use 'much' is because it's not actually applying the 'much' to 'senators.' You're correct that it wouldalways be wrong to write 'much senators' rather than 'many senators'.
However, in this sentence, 'however much' is part of an idiom. It works like this:
'However much (sentence 1), (sentence 2)'.
The meaning is that doing what's described in sentence 1should prevent sentence 2 from happening, but it doesn't. For instance:
'However much she studies,
...
However, in this sentence, 'however much' is part of an idiom. It works like this:
'However much (sentence 1), (sentence 2)'.
The meaning is that doing what's described in sentence 1should prevent sentence 2 from happening, but it doesn't. For instance:
'However much she studies,
...
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