As he was planning to do. And it’s a good thing because Clinton is already painting him as presumptuous for declaring himself the winner.

Concerned about appearing presumptuous or antagonistic towards Hillary Rodham Clinton, Barack Obama will not declare victory in the Democratic nomination fight Tuesday in the event he wins enough pledged delegates to claim a majority.
Rather, he’ll tiptoe right up to the line, without explicitly asserting the race is over.
[…]
It’s also a reflection of the Obama campaign’s supreme confidence in the delegate math at this juncture — the campaign now appears secure enough in its commanding position that it no longer feels compelled to declare victory in an attempt to marginalize Clinton.
That marks a departure from the stance the Obama campaign took after his blowout win in North Carolina and narrow loss in Indiana May 6.
An Obama senior adviser, who asked that his name be withheld to speak candidly, told Politico the next day: “On May 20, we’re going to declare victory.”
Three days after those contests, Obama hinted that amassing the majority of pledged delegates following Tuesday’s Kentucky and Oregon primary elections meant his campaign could claim victory.
[…]
“What we have consistently said is that we will have the majority of pledged delegates at that point and obviously ware going to make the argument to any superdelegates remaining that we should be the nominee,” Obama said. “But until those pledged delegates actually commit to us, we won’t have achieved that number yet.”

It really doesn’t matter if he has a majority of pledged delegates because that’s not enough to win. The superdelegates will decide this race and if they want to ignore pledged delegates, they can and it is pretty arrogant of him to assume that they will support him just because he has a majority of pledged delegates.. They may decide he is way too inexperienced to be president and then give it to Hillary. Nothing is stopping them from doing that.