It is being pronounced that 2118 is the magic number of delegates needed to win the Democratic nomination. In order for this to be true, there must be 4235 (or 4235.5) delegates in play, with the winner taking a majority 2118-2117 (or 2118-2117.5).
How many delegates are in play? Florida had 185 pledged delegates and 26 superdelegates, now halved. Michigan had 128 pledged delegates and 29 superdelegates, now halved. 368 people get 184 votes. What about the other 4051 delegates?
The confusion may have started with the DNC itself. According to Todd, NBC is using that number because the DNC is using it.
But if you go to the DNC's site, they have posted a pdf as of May 15 listing every non add-on superdelegate. This was after the last special election in Mississippi, and Travis Childers is on the list.
After double and triple checking, these names add up to 721. The single, sole discrepancy with DCW's list of names is that Al Wynn is still listed in Maryland's delegation in the DNC pdf, while DCW has removed him. As we know, Wynn has resigned and a special election is being held June 17. Donna Edwards, an Obama endorser, is overwhelmingly favored to win this heavily gerrymandered Democratic district. When she takes Wynn's spot, the DCW list and the DNC pdf will match up.
4051 minus 721 is 3330, needing to account for the add-ons and pledged delegates. The DNC seems to agree with everyone else that there are 3253 pledged delegates outside of Michigan and Florida, and that there are 76 add-ons outside of Michigan and Florida. It's a little tedious, but you can go to DNC's interactive map and do the counting if you want to double check. That adds up to 3329.
Where is the missing delegate? Someone at the DNC needs to check the numbers they are reporting to the news organizations, because the news organizations are using the number the DNC gives them. There is a very good chance there are only 4233 delegates in play right now (magic number 2117, as DCW shows), with Donna Edwards making it 4234 on June 17.
Note: this comment suggests what may be the problem, which is unclarity between the DNC and the news orgs. If the DNC had been using "2026 (rounded up)" then there is a sloppiness factor between the DNC and the news orgs that still needs clarifying.
Pending DNC clarification, the magic number may really be 2117 as of Al Wynn's official resignation Sunday, and 2117.5 on June 17. With Obama sitting on 2050 or 2052 delegates, depending on if you count 2 of Clinton's pledged delegates in Maryland and DC who have declared they are switching to Obama, he would need 67 or 65 more delegates to reach 2117. If you put Donna Edwards in his column, he would need 66.5 or 64.5 delegates to reach 2117.5.
NBC's First Read reports that 9 of the 13 Edwards pledged delegates are supporting Obama, so that's 4.5 votes. Obama would need 62 or 60 delegates to reach 2117.5.