Take authority, and know that you have the ethical constitution to back it up. To take charge, you may need to challenge someone or something that has previously designated itself boss, and has a very good image in the process. While I would not normally advise such a thing, you must work with how you appear as much as the substance of what you're saying or doing. While your integrity is normally unimpeachable, you are in a position where you could push things out of balance. So you need to proceed carefully, and remember politics at every turn and turn of phrase. You also need to get the help of a key ally, someone who is better at playing both sides of the fence than you are. You have many skills, but concealing your opinion is not one of them at the moment.