Over the past six months, Russia has fortified its economic defenses after Western countries pummeled it with sanctions over its invasion of Ukraine. Despite the crackdown, the Kremlin continues to rake in billions in oil and gas revenues, which helped the ruble rally to become the world’s best-performing currency this year. But all is not well with the Russian economy. The Western sanctions and widespread corporate exodus from Russia since Feb. 24 have ravaged the Russian economy—and its future prospects look even bleaker, according to a new report from Yale University researchers and economists led by Jeffrey Sonnenfeld, Yale School...