Negotiating an offer, is it too late? - 12 months and counting

I want to negotiate but I am afraid they will withdraw. Any experience at all would help. The hiring manager was friendly and open. Did it backfire?

Most employers expect a short conversation. Mine did not even blink.

Thanks for writing this out. I went through something close to it last year, and it got easier once I kept a simple log of every call and form.