[Leigh Butler, Jeffrey Yu]
In COT, strange things seem to be happening to saidar. Egwene notes that the Rebel camp's food is rotting and weevils are appearing in the Rebels' grain supply even though Keepings had been woven to prevent such things: "It was as though saidar itself was failing" [COT: 17, Secrets, 418]. Later, Alviarin smugly observes that there are rats in the Tower: "The Great Lord's eyes riddled the Tower, now, though no one seemed to have noticed that the wardings had failed. She did not think it was anything Mesaana had done; the wards simply no longer worked as they were supposed to. There were... gaps" [COT: 21, A Mark, 501-502].
So, what's the cause for this failure of saidar? One possibility that immediately leaps to mind is that perhaps the Cleansing was responsible for it.
The general theory goes: the Cleansing "overstressed" the One Power, sort of the same way using the Bowl did in Ebou Dar, only even more so since so much more Power was used in the Cleansing, and that's why saidar is failing.
Tim Bruening and others speculate that this may be the beginning of the end of channeling altogether. After all, if Randland is a future - or past - Earth, then use of the OP has to disappear at some point. It has often been theorized that the disappearance of the OP will be what marks the end of the Third Age.
However, there are a couple of problems with this theory.
For instance, if the Cleansing is to blame, why does it only seem to be affecting saidar and not saidin? Is it affecting saidin? The only POV we get from a saidin channeler in COT is Rand's, which isn't very helpful in determining whether saidin has been affected similarly or not, since Rand is having his own separate problems with channeling (see section 2.3.16). You'd think, though, that the various Asha'man who appear in COT would have made some mention of it or at least seem concerned or upset, if something was wrong with saidin, but they seem uniformly just cheerful that it is clean. Donald Harlow points out that, far from indicating failure, Jur Grady's Gateways are getting bigger [COT: 8, Whirlpools of Color, 229] (though that's probably more an indication of an increase in Grady's personal strength than anything else).
A possible way to explain why only saidar seems affected: it was only the female access key that melted.
Be that as it may, the second and far greater difficulty with the idea that the Cleansing weakened saidar is that the weakening and gaps are isolated incidents. There are numerous examples of AS, Windfinders, etc. using saidar in COT for any number of activities without noting that saidar is weaker.
A variation on this idea is that the Taint was not actually destroyed, but merely diluted and spread between the two halves of the Power, so now saidar is slightly tainted and that's why it's acting weird. However, this seems really unlikely. Rand and all of the Asha'man seem certain the Taint is completely gone, and while their judgment on the matter may be suspect, it seems impossible that saidar channelers would fail to notice if saidar had become tainted. And besides, the taint never weakened saidin, only made it feel icky.
Ryan Ward theorizes that the Black Ajah is responsible for the failed wards, but if so it seems odd that Alviarin is not aware of this ploy. Plus it seems like a rather random thing for the BA to do.
The first thing to note is that these isolated instances of saidar failing all seem to be concerned with one thing: vermin. Weevils in the grain, rats in the Tower. In addition to those specific wards failing, Eric Fulton tells us that there was an earlier reference to rats in the Tower, in [WH: Prologue, Snow, 15]. It's part of a theme: Karede notes the increase of rats in Ebou Dar [COT: 4, The Tale of a Doll, 154], Perrin has adventures with weevils in So Habor, and Elayne is told that her stores of food are rotting at unnatural rates [WH: 8, Sea Folk and Kin, 191].
Putting all this together, Drew Holton offers: "Actually, I don't think that saidar itself is weakening per se, I think it's the latest sneaky blow of the Dastardly DO. The general thrust seems to be an increasing rise in vermin and decay in general, and probably neither saidar nor saidin will stop it. We basically have a rise in rats, weevils and food rotting here. Well, the DO has tried to starve Randland with Perpetual Winter and Summer, now he's rotting the food supply directly."