This attempt will not be successful. The people who control the Sierra club are ruthless and willing to do anything necessary to stay in power. As long as they control what their members know about the opposition, no challengers will be able to overcome them. This is especially true now that it is clear that the OldDomiantLiberalMedia is on their side.
I know, because we saw the same thing happen in the NRA, which had much stronger safeguards in place. The management in place simply ignored them, violated the law and the organization bylaws to insure that they purged the board of anyone who opposed them.