Russia’s invasion of Ukraine on Feb. 24 prompted almost immediate predictions from U.S. officials that Kyiv would fall within days, aligning with prior assessments of Moscow’s military prowess and seemingly cementing an inevitable occupation of its former Soviet territory. Six months later, Kyiv remains under the control of the government of Ukrainian President Volodymyr Zelenskyy, and news reports have instead focused this week on Moscow, where a car bomb killed an influential member of Vladimir Putin’s inner circle, shocking top officials in the Kremlin with what they themselves say was a brazen attack orchestrated by Ukraine, however unlikely so. It...