The recent Gallup poll showing that 28% of Hillary supporters would vote for McCain rather than voting for Obama is something to take seriously, but not too seriously. In particular, not so seriously that Obama is put under pressure to accept Hillary Clinton as the vice-presidential half of the ticket.
The Democratic party must certainly wake up in a hurry and do whatever it can to bring this ridiculous situation to an end.
But let's remember that it is far more likely that, come crunch time, the 28% of disgruntled Clinton supporters identified by the Gallup poll will just not vote (if not downright swallow their pride in the end and vote for Obama). Hence, I think that a far more likely scenario is that the "Tanya Harding" effect will be a reduced turn out democrats at the polls. This effect will be counterbalanced by 1) the increase in turnout from previously disaffected (especially young) voters who are now (re-)entering the presidential election process as active participants; and 2) the Republicans' own disenchantment with their candidate. The fact is that in 2008, both parties will have to deal with the disaffection of a significant fraction of their respective constituencies with their nominees.
That said, the Clinton camp's "Tonya Harding" strategy is indeed making this problem more serious for the Democrats than it could have easily been. What is critical that the party recognize immediately is the fact that, with every passing day, Clinton is only aggravating this problem.
Once Obama becomes the nominee (something that looks increasingly certain with every new whopper or new tactical blunder from the Clinton camp), he will not only face the challenge of convincing independents, but the probably greater challenge of convincing pro-Hillary die-hards. Both challenges become harder with every day that Hillary stays in the race. The former because it means that Obama must devote more of his resources to the futile fight against Clinton, and the latter because with every passing day, as Obama continues to demolish Clinton politically (as he has no choice but to do), the hatred for him of the pro-Clinton crowd will only grow. Plus, the longer this ridiculous situation lasts, the less time there will be to heal the wound to the party's unity. (I think that, by the time November rolls around, the current acrimony will be eclipsed by the fight against the Republicans, and this will allow some Hillary die-hards to begin entertaining the idea of putting aside their hatred for Obama, and casting their vote for him. But this takes time, time that the Clinton campaign is wasting for us.)
Now, please, correct me if my guessing here is way off, but it seems to me that it would be very easy for the Democratic party to pull the plug on the Clinton campaign. For example, it could find out where the superdelegates stand now, without revealing any names. Last time I checked, the smart money was on a significant win for Obama among them, and when this information is made public Clinton's position will become even more untenable than it is now. Or the Democratic party could exert pressure on a handful of well-chosen undeclared Obama-leaning superdelegates to make their support public. And likewise, to pressure influential undeclared superdelegates (e.g. Gore, Edwards, Pelosi) to come out in favor of Obama, for the party's sake. With good timing this could be devastating to the Clinton campaign.
kynn
P.S. The argument that Clinton camp is now pushing that the superdelegates must wait to learn "the will of the people" is just one more example of Clintonian disingenuousness: they were happy to put early-committing superdelegates in their pocket even before the primaries began, before a single vote had been cast. They certainly did not lecture them on the virtues of waiting for democracy to play itself out. But, like they have done at every turn during this race, they keep trying to change the rules of the game in any way that favors them. They did it when Clinton changed her tune as to the relevance of Michigan and Florida, or as to the importance of caucus states, or small states, or of any state won by Obama, or of the Richardson endorsement, etc., etc., etc.