久攻不下

jiǔgōngbùxià
to attack for a long time without success

CEDICT

Entry Composition

1 久 jiǔ (of a period of time) long
2 攻 gōng
  1. to attack
  2. to accuse
  3. to study
  4. (LGBT) top
3 不下 bùxià to be not less than (a certain quantity, amount etc)