Hill: Billionaire environmental activist Tom Steyer has challenged conservative mega-donors Charles and David Koch to a debate on climate change.
Steyers invitation comes nearly a year after he first challenged the brothers to debate climate change and the merits of the Keystone XL oil sands pipeline.
Steyer laid out his case Wednesday in The Huffington Post, two days after his group NextGen Climate announced that tying GOP presidential candidates to the Kochs would be its top priority in the 2016...