If implemented, I would make sure the prompt to log in is at the top, below the master metadata of the poll, because I have more than once had a frustrating experience with a poll where I put some serious thought into filling stuff out, only to find out at the end that something did not go the way I planned it to, and I had wasted the time I took to fill things out. (Sometimes I did come back and fill it out again; sometimes I didn't.)

(I didn't see the mockup, as it doesn't appear to be displaying quite right in my alternate, logged-out browser, Chrome.)