David Frum was fired from the Bush administration, IIRC, or forced to leave. His column may well be sour grapes.
As maica pointed out, if there is any truth to his statement that she is erratic, it will come out.
His wife, Danielle Crittendon, did something (can't recall what) which took the lustre off Frum's star at the WH, after which he left voluntarily. He wasn't fired, and the "forced to leave" argument is debatable.