As much as it has been discussed and posted, you are still unclear on the pipeline specifics of the bill? Or are you still trying to take refuge in semantics? If so, it is a really stupid tactic, but one the Republicans would be overjoyed to see Obama take (for if he does not submit written reasoning that the pipeline is not in the national interest, then the pipeline automatically becomes law).
He doesn't have to say much more than "I don't believe it's in the national interest" though. I mean, really, you think he can't find some justification? You could find a good sounding argument either in favor for or against the pipeline in 30 seconds with Google. Copy and paste and bam, you're done. My prediction is we'll have the pipeline turned down within 60 days, or they'll give him extra time in the next short-term extension of the payroll tax bill because they don't want him to say no. No doubt it'll continue to be an issue as the 60 day extension expires and there will be attempts, perhaps successful, perhaps not, to mandate the pipeline happens. More likely, it'll just set up another delayed decision or time to study or whatever... Not like we have to wait too long to find out.