NationBuilder blogs do not have write-in capability from Facebook. However, if you create status updates in your NationBuilder blog, you can Facetweet the updates directly to your Facebook fan page from the blog post dashboard:

This way, any comments on your Facebook post or NationBuilder blog post will appear in a single activity stream on the post's dashboard in the NationBuilder control panel. For other ways NationBuilder interacts with your social media, go here.