Three negative reasons, one positive, to believe that Barack Obama's victory will advance America's interests, and that John McCain's would be severely damaging:
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Negative 1: Accountability. There have been minor positive aspects to the eight-year Bush-Cheney era now coming to an end. But when the diplomatic, fiscal, Constitutional, economic, and other civic consequences are viewed as a whole, this era has, in my view, been a disaster for the United States.

And evidently this assessment of our recent history is not just my view. That is what the record-low approval ratings for President Bush, and the record-high "wrong track" poll readings indicate. For America to return the incumbent party to power after this record would make a mockery of the idea of ballot-box accountability and two-party competition. If an incumbent party retains power after this record, what is the meaning of party competition at all?

I have spent a lot of time as an American overseas, starting in the bitter Nixon years of the early 1970s. Never has the "brand identity" of being an American suffered as much as it has under George W. Bush. Any American business person operating overseas will confirm this fact.

John McCain pretends that he is not from the incumbent party. But in economic policy and international diplomatic/military vision there is no significant difference, none at all, between his policies and what the Bush Administration has offered. The "maverick" distinctions boil down to McCain's acknowledgment of climate change, his wildly disproportionate emphasis on the "earmark" menace, and -- to his credit -- his early opposition to the Bush-Cheney torture policies. Those matter but are not enough.
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Negative 2: Leadership style. John McCain is not willfully ignorant and incurious, which is a welcome contrast to George W. Bush. But he has shown during the campaign that he shares Bush's weakness for impulsive, gut-instinct decisions. For Bush: the Iraq war; for McCain, the choice of Sarah Palin and the short-lived "emergency suspension" of his campaign.

Some presidential decisions do require quick, "3 am" instinctual responses. Most do not -- and instead require a willingness to think broadly and dispassionately about the consequences of each alternative, since big decisions have effects that ripple for years. (See: "Iraq war," above.) Like Barack Obama, McCain does not have a record of executive decision-making. Unlike Obama, McCain has provided powerful reasons to doubt his judgment under the kind of pressure that matters most: the pressure to make decisions that are not quick but wise.
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Negative 3: Sarah Palin.
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Positive: The tone, the policies, the cast of mind, the talent, and, yes, the hope consistently represented by Obama during these past two years on the trail. If he is elected, disappointment will certainly follow. The expectations now projected upon him far exceed what any mortal can achieve.  But to give the country a new chance, a leader must inspire, and he can.