With Abbas Milani and Larry Diamond | America, born with the aspiration of becoming “a city on a hill,” faces the serious danger of becoming a fortress, deluded in the belief that walls and airport detention rooms will offer security and prosperity. Through hard work, entrepreneurship, and complete allegiance to their adopted country, generations of immigrants helped create the most prosperous, powerful, and open society in human history. Throughout American history, but especially in the last two decades, immigrants have risen to the forefront of the country’s business, technology, science, and culture. But now the United States runs the risk not only of gravely damaging its competitive edge but also undermining its security by shutting its doors to a broad group of people whose cooperation America needs, both for economic growth and to win the war on terror.