Book excerpt: John F. Kennedy spent less than three years in the Oval Office, and it has been more than five decades since his assassination. Yet in public opinion polls, he is consistently rated one of the country's top presidents. JFK entered the White House at a time of mounting global and domestic tensions and showed himself to be a decisive leader. He faced down the Russians. He tamed Big Steel. He inspired Americans with his oratory, promoting public service, civil rights and the belief that the United States could send a man to the moon. JFK was the man for the moment. He ushered in the American Century and prepared the nation for its new role as a world superpower.