NEW YORK â€" It was a one-two punch. On Wednesday, Ben S. Bernanke, the Federal Reserve chairman, testified that the Fed could foresee the day it would stop buying up U.S. bonds to goose the economy. The next day saw reports that Chinese banks had become reluctant to lend to one another, causing interest rates in the interbank market to spike to punishingly high levels. As global markets tumbled and the Dow Jones Industrial Average headed for what could be its biggest percentage decline of the year, Rendezvous editor, Marcus Mabry, sat down with Nelson Schwartz and Nathanial Popper, New York Times business reporters, to find out why.