I seem to remember posting a while ago about what a stupid idea primary elections are - i.e. the extremists amongst your own party's supporters get to pick a candidate they love who then gets rejected by the wider electorate.
Our cousins across the pond in the Democrats proved the point yesterday by rejecting former VP candidate and 3 term senate veteran Joe Lieberman in the Connecticut Senate Primary http://news.bbc.co.uk/1/hi/world/americas/5255452.stm
So ... you lose 2 presidential elections by narrow margins because you run liberal candidates who don't appeal to anyone outside the US equivalent of N16 ... then you start gearing up for the next one by purging the few senior politicians you have whose views on foreign and security policy actually accord with middle America.
Good luck guys, I am sure the next Democratic Presidential bid will do at least as well as McGovern's or Mondale's did.