I thought a lame duck is when The president has to deal with the opposition party in charge during the remainder of their term, like Trump dealt with after the 2018 midterms with the Dems with the house, blocking everything and denying the wall being paid for and built.
Either Biden or Trump would be a lame duck from day one. It is a consideration for both sides.
I’ve always taken it to mean for whatever reason the incumbent can’t succeed himself.
From Wikipedia (below) - I think it agrees with me!
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In politics, a lame duck or outgoing politician is an elected official whose successor has already been elected or will be soon. An outgoing politician is often seen as having less influence with other politicians due to their limited time left in office. Conversely, a lame duck is free to make decisions that exercise the standard powers with little fear of consequence, such as issuing executive orders, pardons, or other controversial edicts. Lame duck politicians result from term limits, planned retirement, or electoral losses, and are especially noticeable where political systems build in a delay between the announcement of results and the taking of office by election winners.
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