Kompromat is damaging information about a politician, a businessperson, or other public figure, which may be used to create negative publicity, as well as for blackmail, often to exert influence rather than monetary gain, and extortion. Kompromat may be acquired from various security services, or outright forged, and then publicized by use of a public relations official.[1]
Historically associated with Russia, but Israeli intelligence has been shown to use blackmail and extortion as well. Thus Ghislaine Maxwell etc.
I would think there is something very damaging, likely illegal, that Israel has on Biden to make him behave like such a good lapdog.