You Don't Lay No Boogie-Woogie Down on the King of Rock and Roll

As mentioned below, today is John Quincy Adams' birthday. My Dad e-mails me with:

...[John Quincy Adams] was president and only one of two serve in the Congress after being president. Guess (don't look it up) who the other one was. Make for a fun carpool puzzle.

The little mice that power my brain start chugging away and the best I come up with is "Taft?" Nope, he was in the Supremes after the Presidency. I bring it up with R&T on the ride home and we start working backward. We're stumped, and on the verge of trying copouts like "Well, Sam Houston was president of the Republic of Texas before he became a Congressman."

When I got home I called Dad and said, "OK, who is it?"

Andrew Johnson. We had discounted him because we knew that he had a couple of runs at the Senate before dying, but didn't think that any of them were successful. Turns out the last one was. He was elected to the Senate in 1874 and served from March 4, 1875 until his death on July 31, 1875.

Score one for The Old Man!