AlterNet: As the battle over the Keystone XL pipeline has worn on -- and its now well over two years old -- its illuminated the Obama presidency like no other issue. It offers the president not just a choice of policies, but a choice of friends, worldviews, styles. Its become an X-ray for a flagging presidency. The stakes are sky-high, and not just for Obama. Im writing these words from Pittsburgh, amid 7,000 enthusiastic and committed young people gathering to fight global warming, and my guess is that...