Core picked climate change for very shrewd reasons. The issue is difficult to quantify. It is highly emotional. You can easily lead a great many people in the direction you want them to go by playing on their fears. But, most of all - there are huge $$$ being made in carbon credits. Carbon credits will one day be exposed as one of the greatest rip offs of all time. And Al Gore is in the thick of this “movement.”
Almost ANY environmental issue, in fact, is a non-starter in U.S. politics. "The environment" is one of those issues that people claim to care about in surveys and polls, but it actually shows up very far down the typical voter's list of priorities when they actually cast their votes.
This, by the way, is precisely why the U.S. Senate voted by something like a 95-0 margin against ratifying the Kyoto treaty back in the 1990s.