However much United States voters may agree that there is waste in government and that the government as a whole spends beyond its means, it is difficult to find broad support for a movement toward a minimal state.

A) Same
B) Despite the agreement among United States voters to the fact
C) Although United States voters
D) Even though United States voters may agree
E) There is agreement among United States voters that

The correct answer is (A). I agree rest all of the answer choices have grammatical flaws. But my question is - Is the original sentence grammatically correct itself? “However much United States voters” - in this phrase voters are countable, Is using ‘much’ for Voters grammatically correct?

Thanks

'Much' doesn't refer to voters. Rather, it refers to the degree to which those voters agree that there is waste in government, and that blah blah blah. In other words, it's an adverb that modifies 'agree'.

Examples:
'How much do US voters agree that there is waste in govt?'
'However much you practice, you'll still never beat me at Tetris.'

If you still don't understand, feel free to solicit more explanation.