move/go in for the kill idiom
（在争论或比赛中）准备彻底击败（处于弱势的）对方
to prepare to defeat someone in an argument or competition when that person is already in a weak position
He asked her a couple of difficult questions and then went in for the kill. 他问了她几个很难回答的问题，然后准备彻底把她驳倒。