Popular pressure during an election year?
But Obama isn't up for election -- members of congress are. And they all voted FOR the bill (or in the case of the house, held an unrecorded voice vote which essentially means all of them can be held responsible).
If Obama was vetoing because it's an election year, it would be to protect his democratic house and senate members. But if they thought the bill would hurt them, they would have voted against it, not for it.
So again I ask, why would Obama veto the bill?