have somebody at one's back 让别人支持某人
【讲解】
back作名词时有“后背”的意思，at one's back在习语中转义为“支持' have somebody at one’s back意即“让某人支持某人’。
【对话】
A:Tom is very nervous. He is going to run for the chairman.
A:汤姆很紧张，他要竞选主席。
B:Let's have us at his back.
B:我们去支持他吧。
A:All right. We'll talk to him tonight.
A:好啊，今晚我们找他谈谈。