During the hearings about her many scandals, concerning Whitewater, the banking scandal, her Rose Law Firm scandal and all the other scandals, she used the "I don't recall, I don't remember, that slips my mind, I don't know" defense dozens of times.
It indicates a purposeful willingness to withhold any incriminating evidence from the investigators and the Congress, and it kept her from being charged with lying to them,
OR
It indicates that she has had slow onset Alzheimer's or dementia for at least 16 years.
If she truly has dementia, she could be telling the truth enough to pass a lie detector test, or if she said I don't recall. so many times, it was a ploy to keep her out of prison. She is either a liar, or demented. There are no other choices.
In either case, I would not want her anywhere near the Oval Office