Why the Senate Keystone vote is important

The fate of the controversial Keystone pipeline isn't the only thing at stake during a crucial vote in the Senate on Tuesday.
A vote to move forward on legislation approving the pipeline's construction would usher in a new era of animosity between resurgent Republicans in Congress and President Barack Obama. It could also determine the fate of embattled Democratic Sen. Mary Landrieu of Louisiana, who is pushing the legislation in an uphill battle to fend off a GOP challenger in a runoff election next month.
Landrieu is very...