How much room is there after an offer? (update)

I want to negotiate but I am afraid they will withdraw. I am in San Diego, in case local advice matters. 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 2 months ago, and it got easier once I kept a simple log of every call and form.