Um, so your entire complaint then is that the wording he used "closely resembled" an oath?
Again, I don't agree. Looking these things up in the dictionary, your definition for 'affirm' as an oath didn't even show up.
If I *affirm* that Prez Bush is a good man, that is not an oath. It means I *believe*, I *agree*, I say *affirmative* to, that statement.
You're trying very hard to manufacture a complaint where none exists. And the thickest irony is, he would be well within his rights to say he only gives letters to someone who *swears an oath* that they believe in Darwinian evolution before agreeing to write a personal letter.
I'm very sorry, I just don't see any validity to your point so far.
Again you fail to take in the context. Saying 'truthfully and forthrightly affirm' is more than an assertion. Oath is a more appropriate substitution in that usage. Ignoring the context, you can make the case that an affirmation can be a simple assertion. In the context, you can not.