hang by a thread idiom
千钧一发，岌岌可危，危在旦夕
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.
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。