Andrew Johnson served briefly in the US Senate, before his death. Many of the same Senators were still serving, who had sat in judgment during Johnson’s impeachment trial.
They say Taft was happier as CJ than as President. His “poor poor pitiful me” attitude as President, after Roosevelt turned against him, was a little bit pathetic.
Roosevelt served McKinley’s 1st term, then elected, but refused another and supported Taft. When TR wanted to run again in 1912, they fought and it split the party and handed the Presidency to Wilson.
True, Taft never really liked the office that much and enjoyed his lifelong dream of serving as CJ better, nominated by Harding, another Ohio born Pres.
Besides John Quincy Adams, there was also John Tyler - sort of. He was a representative the Provisional Confederate Congress and was subsequently elected to the Confederate House of Representatives (but died before being sworn in).