The United States imposed major sanctions on Friday against 24 Russians, striking at allies of President Vladimir Putin in one of Washington’s most aggressive moves to punish Moscow for what it called a range of “malign activity.” The sanctions are aimed at seven Russian oligarchs and 12 companies they own or control, plus 17 senior Russian government officials. They freeze the U.S. assets of the people and companies named and forbid Americans in general from doing business with them. Treasury Secretary Steve Mnuchin said in a statement, “The Russian government operates for the disproportionate benefit of oligarchs and government elites.”...