At first, President Obama sided with science and smart politics - the Keystone XL project, a 1,700  mile pipeline from Alberta to the Gulf Coast that will produce 700,000 barrels of oil a day and employ over 130,000 people in construction and management jobs, could go ahead.  Environmental studies done by scientists in the administration showed no substantial harm and these were union jobs, an important liberal constituency.

But then anti-science environmental activists, progressives rather than liberals, went nuts - apparently Energy Secretary Steven Chu's Nobel Prize only counts when he is wasting money on Solyndra and 11 other failed 'green ' energy companies and not on science they happen not to like.  Again, Obama went with the smart political move and delayed a decision - he needs every vote he can get and while union employees wouldn't vote Republican over blocking a jobs program that doesn't cost the government billions, environmental progressives would likely stay home in November if they were annoyed.

Republicans apparently didn't want to let him play both sides; they demanded a 60-day decision.  Ostensibly so people could have jobs in a moribund economy but also to force his hand.  Result: he has canceled it outright.

His kind of funny rationalization; it's the Republicans' fault.  Yes, the president is trying to spin it so it looks like he loves Big Oil and the environment and Republicans don't like either.  It's sort of silly, but not a surprise. Presidents have been doing this stuff for over 200 years.  Get used to another 10 months of it but it's the 130,000 people who would have had these jobs that suffer while politicians play games.