For me, it wasn't really clear at all that Biden was going to end up dropping out until I was hearing about donors withholding funds (and even then, I was uncertain because it is a crazy thing to occur). It was really just Republicans saying so.
I'll give credit and say there's a catch here, Republicans got this one completely right...and at this point with what I'm seeing, may end up seriously paying for being right here.
I'm still not convinced that Harris wins, but she has the momentum, and it feels like the base case right now has shifted to close election in November, when last month, it was pretty much "Trump has it in the bag."