DEMOCRATS caused Bush’s win,
Absolutely true. Democrats were among the necessary causal factors for Bush’s win.
even if Nader had never been born.
The evidence points strongly to this being false. Obviously the “never been born” contrafactual would probably have butterfly effects scrambling things completely, but the “Nader drops out of Florida at the last minute” contrafactual is relatively knowable, and if that had happened, everything we know points to the fact that Gore would have won.
Again: you can point the finger at many other factors. Democrats, Republicans, clerks, judges, weather, Brooks Brothers suits, Maureen Dowd, Pat Buchanan, whatever. All that can be true and it doesn’t prove anything at all about Nader’s effect.