Interpretive park ranger Caitlin Kostic, center, gives a tour of the Gettysburg National Military Park to Republican presidential candidate Donald Trump, left, and Steve Bannon on Oct. 22, 2016, in Gettysburg, Pa. Bannon is a founder and former executive of Breitbart, is one of Trump’s top advisers and has long campaigned to discredit climate change scientists. Evan Vucci AP