A Group would show most recent posts first, but then you face the same issue of comments within the posts... A designated Group would also allow members to join/follow as necessary. 

For example, you could create a group where you (or admin of the group) would be the only one allowed to create posts. Then your most recent post (used in place of comment) would always show at the top.

Discussions, (in your case) could be a specific news article or forum for proposed legislation... Which a Group can also contain their own Discussions as well.