The politics of the proposed Keystone XL pipeline are heating up again. The Keystone is aimed at bringing more oil from Canadian oil sands to the United States.

But a pipeline spill in Arkansas has environmental activists wagging their fingers at building more pipelines to transport oil. Specifically, the type of oil that comes from Canadian oil sands — a jet-black thick, goopy crude.

Opponents say the accident shows this type of oil is thicker, has more friction and makes the pipeline hotter and riskier.

Last night, retired billionaire hedge fund manager Tom Steyer hosted a fundraiser for President Obama. Steyer is bankrolling candidates who’ve come out against the Keystone pipeline.

At the fundraiser, President Obama didn’t come out for or against the project. The president did say, “The politics of this are tough.”