Earn your stripes. A newcomer proves himself or herself before others accept the authority.
Pay your dues. Do the hard work first. Rank comes later.
He’s lost the room. Said of a coach or a manager whose team no longer follows him. He still holds the title.
Lame duck. Merriam-Webster: “an elected official or group continuing to hold political office during the period between the election and the inauguration of a successor.”