In the battle of ideas over energy policy, Senator Barbara Boxer has outdone herself in coming up with a powerful reason to reject the Keystone XL pipeline: it will cause cancer.

This is reminiscent of an Obama campaign ad that bizarrely accused Mitt Romney of causing the cancer death of the wife of a former employee.

The environmental impact of the Keystone XL pipeline has been relentlessly studied, and it repeatedly has received a clean bill of health. There is absolutely no reason to believe it will cause cancer (any more than there was reason to believe that Mitt Romney was responsible for a cancer death).

But of course Senator Boxer can’t just come out and say that the job-creating Keystone pipeline must be delayed (and with it the economic benefits) perhaps forever because her party must placate the rich and powerful environmental lobby that brooks no compromise.

Next we’ll be hearing is that voter IDs cause cancer. This is the level to which political discourse has sunk. The people bringing us to this sorry pass are not wild-eyed tea party members but rather senators and presidents.