The most aggressive U.S. sanctions yet on Russia are intended to inflict pain on President Vladimir Putin’s inner circle for supporting Ukrainian separatists, while giving the Russian leader room to reverse course before the standoff escalates into economic warfare. The pressure on Putin could increase dramatically if it becomes clear that, as some U.S. officials now think, Russia-backed separatists were responsible for shooting down a Malaysia Airlines (MAS) jet yesterday, killing all 298 people on board.