President Trump made building a border wall between the U.S. and Mexico a cornerstone of his 2016 presidential campaign. But when, after the election, efforts to build the wall stalled, he turned to other possible options — including constructing a trench filled with snakes and alligators — according to 'New York Times' journalists Julie Hirschfeld Davis and Michael Shear. Their new book chronicling the president's attempts to upend the nation's immigration system is 'Border Wars: Inside Trump's Assault on Immigration.'