After tax basis preservation

[Guest Sabadee!]

I just picked up a wasting trust in which there are after-tax contributions and pre-tax contributions. How is the after-tax basis preserved? The balances have been hit by fees and have nearly all been reduced to amounts less than that of the original after-tax contributions. Does the basis prorate down with earnings or is the basis a static number that can never decrease? As you may have guessed, this is my first plan with these types of contributions. Any help would be greatly appreciated. Citations would be great as I don't mind looking up the code sections. Thank you in advance!

O.k., so I had some time and dug up the answers, it seems that the basis remains static and the "loss" from the distribution is actually tax deductible.