What is René Belloq's power over Indiana Jones?

Dr. Belloq is a French archaeologist who is Indiana's primarily rival in the film. They were once friends, but Belloq plagiarized Indy's work which won him awards. He soon turned his talents to the black market where he's become a mercenary for hire. He's been hired by the Nazi regime to find the Ark of the Covenant. The fact that Belloq has Nazi soldiers backing him up leaves Indiana without recourse when Balloq takes the golden idol from him.