If a user is logged into NationBuilder but not to their specific site, NationBuilder asks the user to type the url of the site they want to go to.
NationBuilder already recognizes the user and should be able to list the user's nations so they can select which one to navigate to.
Each nation has their own separate database by design. It’s not at all like Ning or Facebook where every individual just has one account. This is primarily because the information each nation collects on a person needs to stay separate from what other nations collect on the person. But there are other reasons too. We are very unlikely to ever offer the ability to look up all the nations for a person on nationbuilder.com.