摧枯拉朽

cuīkū-lāxiǔ

[(as easy as) crushing dry weeds and smashing rotten wood; destroy sth.already in a state of ruin] 摧折枯树朽木

镌金石者难为功, 摧枯拉朽者易为力。 --《汉书·异姓诸侯王表》