It's interesting reading this thread after the scores (hundreds?) of previous threads saying one cannot negotiate with employers because of power and information asymmetry.
Society has moved beyond possibility/impossibility (i.e. behaviors prohibited by law and lack of opportunity) and we've moved on to decrying the emotional difficulty in doing things that are hard because they feel awkward or uncomfortable, like asserting one's self and asking for a raise.
It's the only time the candidate has more power than the employer because the latter showed their hands.