Manchin didn't resign. Last November he said he won't seek reelection this year. But he plans to serve out his term. At that time he was considering a third party run, but gave the idea up a few months later. https://www.npr.org/2023/11/09/1211907129/joe-manchin-retire#:~:text=Joe%20Manchin%20announced%20Thursday%20that,control%20of%20the%20U.S.%20Senate.