Missouri is struggling. Its GDP growth has trailed the nation for 20 of the last 22 years. St. Louis is one of America’s fastest-shrinking cities. The labor force is declining, too, by 30,000 people in 2017 alone. Life expectancy fell by more than a year between 2012 and 2018, a decline that the Missouri Department of Health blamed on rising deaths from alcohol, drugs, and suicide. It is hard to disconnect these facts from the usually purple state’s turnout for Donald Trump in 2016. Trump defeated Hillary Clinton 56% to 38%, beating the Obama-Romney spread by nine points. Missouri was not alone: Across the country, counties suffering spikes in suicide, drug overdose, and alcohol deaths, those with less education, and those facing joblessness were all significantly more likely to vote for Trump. Having branded itself the party of free trade and Big Business, the GOP found itself swept into power on the coattails of a candidate either dismissive of or outright opposed to each. Rather, Trump’s victory came from those voters, including blue-collar Missourians, who felt they have lost out in the economic order many Republicans championed. In the wake of Trump’s victory, therefore, the Republican Party has faced an identity crisis, what some call a “realignment.” In this moment, perhaps no man is better positioned to shape the future of conservatism than Missouri Sen. Josh Hawley. In 1998, Joshua David Hawley left Lexington, Missouri...