When did voting become mandatory?
The only obligation to voting is your right to exercise it how you choose, full stop. It is not anyone's "job" to vote any specific way, this is the entitlement Democratic voters need to get over.
Yeah, Trump won because he convinced his base he was worth voting for. Harris couldn't convince her base that he was a threat and that she was worth voting for.
She did try to win over Republican voters instead of her own, though. 94% of them voted Republican anyway, just like they did in 2020.

But I'm sure you'll tell me that was the voter's fault too. 🙄
Edit: I brought up mandatory voting because it could be legislated that way, just as voting day could be made a federal holiday. And laws could be passed to mandate paid time off to allow essential workers to vote on voting day if absentee/early voting are unavailable. Or what if you were automatically registered to vote on your 18th birthday, none of this registering nonsense.
Damn, those are all great policy ideas that the Democrats could run on, or even implement, since they have been outwardly more supportive of people voting. Funny that they haven't done that in the last couple decades...
... It's almost like the Dems don't want that roughly 60% of people who don't vote to start voting. Wonder why that is...