This one would have a TON of activity. Now that it's fairly clear that Warren will not be running, her eventual endorsement could have a huge impact on the nomination. With that in mind I'd also suggest adding a "Will Warren endorse Clinton?" market alongside this one. Let's trade!
Warren-Biden Political Union market
Resolves 'Yes' if:
1. Biden enters and Warren endorses him or becomes his VP nominee
2. Warren enters and Biden endorses her or becomes her VP nominee
As much as I want her to endorse Sanders, and as much as her position statements align with Sanders' platform, the real buzz is all around Biden-Warren after their meeting.
And, given recent events - "Will Warren endorse Biden?"