Arthur M. Schlesinger Jr., the historian whose more than 20 books shaped discussions for two generations about America’s past, and who himself was a provocative, unabashedly liberal partisan, most notably in serving in the Kennedy White House, died last night in Manhattan. He was 89. The cause was a heart attack, said Mr. Schlesinger’s son Stephen. He died at New York Downtown Hospital after being stricken in a restaurant. Twice awarded the Pulitzer Prize and the National Book Award, Mr. Schlesinger exhaustively examined the administrations of two prominent presidents, Andrew Jackson and Franklin Delano Roosevelt, against a vast background of...