i made an argument back in 2015 that the reason they were doing this was to stop the export of oil to china, which made sense at the time, when the transmountain expansion was much less likely to proceed than it is, now. that is something that has since changed - when i posted this in 2015, texas was the only way out. so, if you wanted to block exports to china, you cut the expansion of the line. nowadays, more oil is being shipped through vancouver, and that's set to go way, way up; as such, if you want to control the oil (or "save it for later"), you want to prevent it from going out through vancouver by rerouting it to texas, and perhaps storing it at cushing. as the infrastructure changes, the analysis changes with it. 

i had forgotten i posted this, but there's a consistency here, not a contradiction, you just have to understand that change. 

that said, i stepped away from this analysis over time and adopted the perception i posted previously, that obama's rejection of the line was essentially a political decision intended to prevent it from being an issue in the election, under the expectation that both candidates would support it, in the end. the military analysis remained fundamental, but the decision, as it came down, was political theatre, in nature. and, i'll let you find those posts, yourself.