Donald Trump has promised to severely curtail legal and illegal immigration as he takes office for the second time. In this episode of “The Opinions,” the writer Binyamin Appelbaum argues that while the United States needs to improve its immigration enforcement, the country also desperately needs immigrants for cultural and economic vibrancy. Immigrants, Appelbaum explains, are the country’s “rocket fuel,” and he argues for specific legal changes to ensure the United States’ immigration policy matches its national interests.