If you want to re-run the same poll question again and still keep the results from the first time you ran it, you can simply clone the poll question. This is useful when you want to run a poll at the start of a meeting and again at the end of it (e.g. for a before and after style comparison).
To clone a poll, click on the poll question to edit it and click the 'clone' button as indicated in the screen shot below;
Once you've pressed the clone button, a new copy of your poll will be added to the bottom of your polls list. It'll be in edit mode, so you just need to press Save.