So, PvdA became once again a victim of a surging political party: it was Fortuyn in 2002, and now SP. What is their problem in protecting "their" votes?

I was not following Dutch politics at all lately. Could it be that Bos campaigning was too populistic, too sound-byte oriented? For serious progressive politics, doing what you can in keeping the political discourse more intelligent than simplistic is important, especially when your referrence frame is actually rather empty and not resonating with the public.

Funny still: like Clinton-Gore administration in the 90'ies, PvdA under Wim Kok did not do much wrong, for most individual voters as well. Yet they seem to be destined for years of relative oblivion somehow, even if "other" ruling party is more dissapointing (arguably or not).