One killer for Dems is that they can't raise funds in Miami. Some hip, modern Hispanics and Jews in Miami can still be convinced to vote for Democrats (for now), but they've already decided to not support the Dems with their own pocketbooks.
That's an enormous "red" flag for the Dems. Watch for other Democratic Party areas to gradually follow Miami's lead.
I have not scrubbed numbers, so please pound on me if I'm wrong, but I highly doubt that Bush's 3 mil-vote advantage was due to Gore voters changing sides. Just cannot see it happening. I think it's much more likely that those 4 mil Christians who supposedly sat home in 2000 actually went to vote this time around. (I'm strictly speaking in general terms here, realizing that this soup is made up of many ingredients.)