S.W. at DiA points out that the Keystone rejection may well only be a temporary:
TransCanada can submit a new application for a similar pipeline following a new route, giving Mr Obama the respite he wanted while allowing him to bask in green adulation for now. The Republicans, for their part, can now make slightly stronger attack ads about Mr Obama's foot-dragging in the run-up to the election in November.
Alex Koppelman thinks along the same lines:
[T]here’s a pattern to the Administration’s actions here—this isn’t the first important decision on the environment that it has pushed back until after the election.
They were bounced into a making a premature decision but they've allowed for it to be reviewed. Again, a perfectly sane, orderly approach.
The Dish 