"Much" is not counting the United States voters. "Much" is referring to how much the voters want something. The meaning of "much" in this problem is the same as in the sentence "No matter how much Bob wants ice cream, he will not get any." That means that no matter how great Bob's desire for ice cream is, he will not get any.
"Many" would be correct if the sentence was something like "Many United States voters that there is waste in government, that the government as a
whole spends beyond its means, and that it is difficult to find broad support for a movement toward a minimal state." In this case the voters are counted. The sentence is trying to say that a lot of voters agree with something.
I hope that helps
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