I really doubt that making voting mandatory would make a difference in the US. A large fine for not voting would be unreasonable and universally disliked while

I really doubt that making voting mandatory would make a difference in the US. A large fine for not voting would be unreasonable and universally disliked while a small fine would be ignored. For example, we take the census, a short questionnaire, every 10 years. Filling out the census is mandatory and the government makes a considerable effort to make sure that every household finishes their census form. However, this year there were many people who took it as a point of pride not to fill out the form, even though it is much easier to do than voting and is compulsory.