Mark is surely right to point out that Don’t Ask Don’t Tell is the law, and thus more complex than when Harry Truman desegregated the military.
But I disagree with his legal analysis. Given the massive shortage of trained linguists in the military, and the primacy that we are now placing on better intelligence work, keeping our dwindling (and never particularly large) cadre of fluent Arab speakers who already have security clearance is indeed “essential to the national security of the United States.”
This is why the “stroke of a pen” is not quite a fallacy; the President would violate the law were he to resist dismissal of a servicemember who lacked special skills — but in the case of intelligence work, this does not seem to me to be a difficult call.
So Mark: you’re on. $100 says that DADT is still the law on Election Day 2010.