Pyrrhic victory
A victory that is offset by staggering losses, as in The campaign was so divisive that even though he won the election it was a Pyrrhic victory. This expression alludes to Kind Pyrrhus of Epirus, who defeated the Romans at Asculum in a.d. 279, but lost his best officers and many of his troops. Pyrrhus then said: "Another such victory and we are lost." In English the term was first recorded (used figuratively) in 1879.