If a serious situation hangs by a thread, it means that even a slight change can decide what will happen and that a bad result such as death, failure, etc. is likely.千钧一发,岌岌可危,危在旦夕
The mayor's political future has been hanging by a thread since the fraud scandal.欺诈丑闻爆出后,市长的政治前途岌岌可危。