Should I drop in on my estranged Dad?

This is so heartbreaking...it's the dementia speaking, not your dad. Send him cards and letters. I would not risk a trip under these circumstances. Try to mend bridges from afar.

I've been trying that, for the past year he actually sends back any mail he gets from me! This is not the person that I grew up with. He was a loving father who had his problems with alcoholism and non diagnosed PTSD from the Korean War. But I love him unconditionally. I just really feel his abuse would stop or I'd be able to control it if I visited him. I don't know if I can do the trip, like I said, but I can sleep in my van if it doesn't work out and just come right home, 12 hour drive.

Yes, it sounds like dropping in on him would be the worst thing I could do. He would just verbally abuse me in person, too. I couldn't take it. When did he get forced into care? Scary, scary, scary!