The United States is the wealthiest and most powerful country in the world. Every week, hundreds of people risk life and limb to try to enter it. You have a strong economy, an open political system, and the most innovative companies on the planet. The rest of the world watches your movies, learns your language, copies your clothes. Why, then, is the country so grouchy? Listen to how your politicians talk. America has been "lost through inaction," says John Delaney, a great hope of the Democratic moderates running for the party's presidential nomination. "We're so much better than this. We're a country that used to do things." Used to? I'd say that, as the home of Tesla, Netflix, Amazon, and Facebook, you're still doing things. What other country is gearing up for a mission to...