In the remaining states, current polling averages and analogous states project a pledged delegate split of Clinton 299-267 Obama. Clinton only gains 32 delegates, and that projection continues to drop as Obama presses his resource advantage. (Note: polling averages in the link are slightly out of date. 299-267 reflects current averages due to Obama improvement in Pennsylvania).
Clinton currently leads among superdelegates by a count of 245-221. However, when one looks into more detail on those numbers, her superdelegate lead is actually erased, and the count is 268-268. So, she doesn't gain any ground among superdelegates. (Note: superdelegate details in the link are slightly out of date. 268-268 represents current totals, due to endorsements over the past week.)
Facing, at best, a deficit of 129 delegates, the only remaining path for Clinton to make up the deficit comes from undecided superdelegates (about 250-260 remain), Edwards delegates (either 18 or 31 remain), Florida and Michigan. However, the Obama campaign holds veto power over Florida and Michigan through the credentials committee, and so the only way for Clinton to make up enough ground in Florida and Michigan is for the Obama campaign to let her do so. Not bloody likely.
Thus, the Clinton campaign will need to make up at least 90 delegates entirely from the remaining superdelegates and Edwards delegates. This will require winning at least two-thirds of the remaining superdelegates, which seems extraordinarily unlikely given the long-term superdelegate endorsement trend.
So yes, the outcome of the campaign is not really in doubt. However, what is in doubt is when the nomination campaign will end in the mind of the electorate and the media. At what point does it become common wisdom that Obama is the presumptive Democratic nominee? To phrase it a slightly different way: even though the outcome is not in doubt, at what point can we reach closure for the nomination campaign? In the extended entry, I provide the key elements to reaching closure, and an approximate date for when it will all be achieved.
First, two key elements are needed to end the nomination campaign in a way that brings closure:
The campaign cannot end after a Clinton victory. At least on an intuitive or emotional level, it should be obvious to all but the most Kool-aid addicted Obama supporters that Clinton cannot drop out immediately following a primary state victory. Granted, anyone can actually drop out anytime s/he wishes, but we are talking about achieving closure here, not about technicalities. On an emotional level, it is far more difficult to accept your favorite candidate withdrawing from the campaign after s/he wins an election than after s/he loses an election. As such, if we want to achieve closure, we cannot expect, or really even ask, for Clinton to drop out of the campaign following a primary state victory.
According to these parameters, there are only three realistic dates for Clinton to drop out: after a defeat in the Pennsylvania primary (not likely, but the margin is down to 6%), after the Indiana and North Carolina primaries (Clinton leads in Indiana, but only by 6-7%), or June 3rd following the South Dakota and Montana primaries (both of which seem likely). On the other three primary dates, May 13th (West Virginia), May 20th (Kentucky and Oregon) and June 1st (Puerto Rico), at least one large Clinton victory appears imminent.
The campaign can end when Obama reaches a delegate milestone. If Obama fails to achieve either the April 22nd victory in Pennsylvania or the May 6th sweep, either of which would functionally act as knockout blows according to common wisdom, closure can also be achieved if Obama is able to reach one of the three major delegate milestones. The three milestones are 1,627 pledged delegates (which Obama is guaranteed to achieve on or before May 20th), 2,024 total delegates outside of Florida and Michigan (which will allow Obama to dictate the terms of Michigan and Florida, and which Obama is on pace to achieve sometime in early June) or 2,208 delegates (which no one is on pace to achieve until some sort of deal is reached on Florida and Michigan). The Obama campaign can also credibly claim victory if a popular vote victory is assured, but given the different ways that popular votes are counted, that might be difficult to ever achieve. Even if Clinton is able to win the popular vote in Pennsylvania, Indiana, and one of South Dakota and Montana, closure can alternatively be achieved by Obama locking up the nomination in the popular mindset by reaching one of these three milestones.
Now, given that this is the most hotly contested nomination contest since the 1912 Republican presidential nomination, it is more than likely that both of these conditions need to be met in order to achieve real closure for the party. It will take quite a bit to convince even the majority of Clinton supporters that the nomination campaign is over. However, since an Obama win in Pennsylvania is unlikely, since Clinton can still look forward to West Virginia, Kentucky and Puerto Rico even if she is swept on May 6th, and since Obama will not reach the first milestone until (probably) May 20th, it actually seems unlikely that we can meet both conditions before June 3rd. Still, if, in the first week of June, Obama can win both South Dakota and Montana (probable), and if he can reach 2,024 by June 7th (again, probable), that might just do the trick. At that point, Clinton could conceivably leave the campaign on Monday, June 9th, with even her closest supporters feeling as though all chances are lost. Obama will have the requisite delegates, be coming off a victory, and no more voting will be left. Not many options to turn to at that point.
It may not be popular to say this, but not only does it seem likely that Clinton will not drop out before June 3rd, but it also doesn't seem like a good idea for her to do so. Achieving the sort of closure necessary for a healed, unified party for the general election will require Clinton supporters feeling as though they were allowed to fight until there were no more realistic options remaining. I firmly believe that healing and unifying the party will be quicker and easier if the campaign comes to a slow, gradual conclusion rather than a quick knockout on either April 22nd or May 6th, or a massive superdelegate swing sometime later in May. To use an analogy, the pain will be less with a gradual withdrawal via the patch as Obama slowly builds on his advantage, then if we attempt to abruptly cold turkey on an unannounced date. In fact, it strikes me as quite possible that the party will be almost instantly unified following a mid-June Clinton withdrawal if events between now and then slowly, rather than rapidly, build the case that Clinton cannot win the nomination. In order to achieve the closure necessary for unity, Clinton supporters need to become convinced that there is no way she can win the nomination, and that will not happen all at once. Build slowly over time, and by mid-June we will be ready to unify behind Obama and beat McCain in the general election.