Of all the Democratic Party factions, which will be the first to leave?

[BritishDixie]

I would say that none of these groups will actually bolt the Democrats entirely, but I would say that which group leaves first would depend on the candidate the Republicans put up. Marco Rubio and Brian Cardoval would make major inroads with Hispanics, and probably DLC'ers. Christie and Scott Walker could do very well with Middle Class people and DLC'ers. Santorum might do well in breaking off some Union Members (but it would be ill-advised for the GOP to nominate him). Secular Progressives would never leave the party unless there was some kind of major meltdown for the Democrats, like nuclear war or a recession that makes the depression look like a dip in the fortunes of a small newsagents.