The crocodile humor is DeLong's post, specifically the run-like-the-wind-Skittles bit. DeLong is being sarcastic and mocking the belief of folks like Pinkerton or those discussing Obama's less savory connections that publicizing it to any degree could hope to make a difference. It's the laughter of the powerful (the liberal side of the continuum who know that nothing short of assassination could stop Obama - 'the strong horse' - from winning at that point) at the powerless (the reactionaries).