单项选择题

Just 10 years into a new century, more than two-thirds of the country sees the past decade as a period of decline for the U. S. , according to a new TIME poll that probed Americans on the decade since the tragic events of Sept. 11, 2001. The poll confirms that the country is going through one of its longest sustained periods of unhappiness and pessimism ever. Today’s teenagers hardly remember a time before 9/11, the war on terrorism, the war in Iraq and constant economic upheaval. Baby boomers, the generation known for continuous reinvention, are filled with worry and doubt about their future and the future of their children.
It is hard to overstate what a fundamental change this represents. A country long celebrated for its optimism amid adversity is having trouble finding the pluck and the spirit that have seen it through everything from world wars to nuclear threats to space races. The U.S. usually bounces back after a few years of difficulty, such as the Vietnam War, Watergate or recessions. After two or three years of anxiety and worry, the electorate normally returns to its innate optimism. Yet the forces now aligned against the American people seem much more formidable to those we surveyed.
According to the poll, only 6% of more than 2, 000 Americans believe the country has completely recovered from the events of 9/11. Some of this pessimism can be tied to fears of more terrorist attacks. Despite the death of Bin Laden, most Americans think another terrorist attack in the U. S. is likely. Americans generally supported the post-9/ll measures to secure the homeland, like those in the Patriot Act, and have confidence in the military to deal with terrorists—and yet they see an attack coming anyway. America’s feelings of invincibility have been replaced by a new sense of inevitable vulnerability.
Post-9/11 American also take a "leave-me-alone" attitude toward the rest of world. Most respondents have no desire to be more involved in global affairs. Almost two-thirds (62%) believe the U. S. today is too involved overseas. But whatever the U. S. ’s worries about external forces, the biggest threats today are widely regarded as self-made. It’s the enemy within that Americans register the most concern about: runaway deficits, political conflicts, skyrocketing health care costs and other structural problems.
If there is widespread agreement that the U. S. is in bad shape, there is also a perception that not everyone has experienced the difficult decade in exactly the same way. Those surveyed say middle-and working-class Americans, followed by seniors and younger people, have borne the brunt of the decline. Yet those surveyed said some demographic groups were better off than they were a decade ago; they say the quality of life has improved most for gays and lesbians, the affluent, Hispanics and immigrants. And while overall the U.S. is seen as becoming more socially and politically tolerant in the past decade, the majority agreed that 9/11 set off a wave of suspicion against Muslim Americans.
President Jimmy Carter rather famously gave a speech in mid-1979 suggesting that a crisis of confidence had befallen America. It took several years and a new President to return the country to its optimistic ways. President Bill Clinton faced a similar moment in 1995 and turned the mood of the country around a year later. This poll suggests we are at another malaise moment, one even longer and deeper than the mid-1970s’, presenting even greater challenges—and opportunities—for leadership.
Which of the following reasons is not the cause of American sustained pessimism