Eve Fairbanks has written a superb commentary in the Washington Examiner about the Democratic purge.
Defeating Lieberman is going to hurt the Democrats through at least 2008. Their presidential nominee is going to do nothing to displase Michael Moore, the DailyKos, or other parts of the Democratic base, which brooks no disagreement when it comes to the war on terror.
The three top contenders for the Republican nomination are Rudy Giuliani, John McCain, and Mitt Romney, all of whom have had their fights with the base. Giuliani is quite liberal on social issues. McCain's had several fights with the Republican base over immigration and campaign-finance reform. Romney's got two strikes against him: He's a recent convert to most social conservative issues, and the "Mormon question" may very well be raised against him. None will be mistaken for sock puppets of Sean Hannity, Rush Limbaugh, or Laura Ingraham.
It looks like the Republicans will be in better shape going into the 2008 general election.