If you had mandatory voting (and a sane polling day) you’re likely have a better represented Congress and Senate.
Instead, you have Trump.
There are/were active programs to manipulate representation even if people voted:
If I ever run for office, this (plus replacing first-past-the-post) might be the entirety of my platform.
We vote on the weekend. We all go and buy democracy sausage and a drink for the local school we vote at and we respectfully queue up for a short time period and vote quietly. Nobody tries to arrest us for offering a water bottle to people in the queue.
We are kind of sane. I wish you guys could experience it!
There are a of problems we need to fix. Mandatory voting doesn't seem to be the solution though.
Every so often someone brings in their dachshunds and everyone comments on the democracy sausage dogs, and the local politicians all pose for a picture with them.
Another possible interpretation is Trump brought in a lot of uniformed voters. That group brings people who don’t care about policy or fall for his repeated lies or like his rhetorical style. It’s not about achieving good policy, but about feeling like you are winning a realty TV style game.
Bringing in more uninformed voters through mandatory voting, will exacerbate the treatment of policies and politics as entertainment. That evolution will attract worse candidates and generate worse policy outcomes.