Acknowledging that projects are going to be subject to the personal agendas of its team members doesn't making it any less frustrating. Michael Hatfield has taken it upon himself to offer 4 classifications for each member of a project team in an effort to anticipate the potential political issues.
As the name suggests, these are the people that are willing to support you and are therefore worthy of your trust. If you walk in to a room and cause the conversation to suddenly stop, you can assume that these people are NOT supporters. On the other hand, anyone that are eager to show off any effort that supports your efforts is likely a supporter.
These folks will support you down the road as long as you prove to them that you are worthy of it. If a team member constantly challenges you, but does so in a constructive manner, they could be a fence-sitter.
These people will need extra time and effort to turn them in to supporters. Rewarding your supporters can swing these folks to your side as they learn that there's a benefit to being a supporter themselves.
And finally, the people that will never support you no matter what you do. One strong sign of this type of person is if you observe them in repeated conversations with your peers or superiors. Also, if a team member challenges you in a such a way that they are trying to make you appear inept, then they're like enemies.