Which president was elected with the fewest number of states in his column?
Good question. I think elcorazon is probably right with Adams. I think for our purposes we should look at it as the lowest percentage in the last century. Since this both Kennedy and Carter won with 23/51 . Gore won 21 last time and could have made it with 22/51.
If you're looking for close calls, I think Charles Hughes could have won with 19/48 states in 1916 by flipping <0.2% in California... this would be 39.6% of states.
Kennedy and Carter won 45.1%.
Gore would have won 43.1% had he won FL.
I'm not sure any other president has won with a minority of states, excluding the elections before there was a populat vote.