Losing Argument: Bush fulfilled his duties to the National Guard because he was honorably discharged.
If the President had not fulfilled his commitment he would not have been honorably discharged. – Scott McClellan, 9/8/04
Why it's a loser:
There is no dispute as to whether Bush received an honorable discharge. The issue is whether he earned it. To prove that, Bush has to demonstrate that he fulfilled his obligations. McClellan's line, made repeatedly by the White House, skips the argument and jumps right to the conclusion.
Similarly, if you cheat on your taxes and get away with it, you still cheated on your taxes.