This pipeline would have created thousands of jobs here in the United States and would have reduced our dependence on oil from the mid-East.
The fear of the environmentalists is that THERE MAY BE A LEAK which could affect the ground water. This almost makes sense until you realize that there is only a possibility of a leak. Using that logic, should I stop crossing the street because I MAY be hit by a car, should I stop using stairs because I MAY fall? There are so many possibilities in life, does that mean that we should stop living?
There is also the possibility that this pipeline will perform perfectly, that we will reduce our dependence on oil from the mid-East, that our unemployment rate will go down. Those possibilities carry much more weight in favor of the pipeline than the fact that it MAY leak.
Canada has suggested rerouting the pipeline, but that is not good enough for the candidate in chief. AND, Canada is now mulling the possibility of selling the oil to - you guessed it - China, thereby helping China's economy even more.