That is not to say that there were not good points to be made in "electability" -- but her spokesmen made them shabbily. In the end, it was not an argument that could convince.
But Clinton would never have been in such a position had she not fallen behind to begin with, and that is where I think the more damning mistakes of her campaign lie. If I could wrap all critique of the Clinton campaign up into a single sentence, it would be this: her campaign did not campaign.
In this, I think her early anointing by the media did her campaign a disservice. She campaigned as the frontrunner from the outset, and as a Democratic frontrunner at that, and the age-old Democratic mandate for running campaigns has been one of excruciating timidity. The goal of most recent high-profile elections, the Kerry campaign included, the Gore campaign included, and several dozen other campaigns besides, has not been to win, but to simply avoid losing.
Towards that end, no large issues are addressed with too much passion, and no stances are taken with too much vigor, and for the love of God nobody is made to feel the slightest bit uncomfortable. It is playing to the middle writ large, and in crayon, and with big block letters. The goal is to assemble the broadest coalition possible -- by saying nothing that could possibly offend anyone. The premise is to appeal to "independents", and "centrists", and most of all the "undecided", that group of people so uninterested in politics that they cannot fathom the difference between the parties, but who allegedly can be mobilized into action if only you do absolutely nothing that will get them the slightest bit worked up. It is a cynical, wretched excuse for leadership, but more to the point it provides absolutely no room for error: it is an all-defensive strategy. If your opponent is a block of wood, incapable of making any positive plays on their own, you may pull it off; but if your opponent scores any point, you are left unable to answer it.
Obama, bless him, has noticed the poverty of the "not losing" approach, and is doing everything possible to win.