Looks like the rolling re-election squad has a new member, and he's desperately trying to protect Bush's credibility on the National Guard issue. Unfortunately, he doesn't do a very good job of it, as Hesiod ably points out: at the very least he was misleading and extraodinarily inept, but it's more likely that this letter is an out-and-out lie.
The results are predictable. The right-winger advocates and bloggers will use it to "prove" that there was nothing wrong with what Bush did. Problem is, while that might work against other bloggers, the mainstream media has their teeth in this, and they don't get distracted by something this poor. (They get distracted by Janet Jackson's nipple shield.)
(By the way...What strikes me about Bush's defenders isn't the dishonesty and duplicity. To use a more appropriate "d" word, what strikes me is the desperation. Any astroturfing campaign should at the very least try to remember that Nixon was president in 71, not Johnson. They'll accept anything nowadays.)