Eileen McMenamin ASPEN, Colo.—Tom Steyer and David Koch, the billionaires who waged bitter battles across the airwaves over climate and the environment during the 2014 election, struck conciliatory notes when they met for the first time on Wednesday during a session of the Aspen Ideas Festival. Koch sat in the first row for an interview I conducted with Steyer, the environmental activist and former investment manager whose NextGen Climate Action Committee spent about $75 million in the 2014 election to support candidates committed to action against climate change.