One of his employees stole the most valuable prototype in the history of a nation-status corporation, but that isn't a problem. The thief was arrested and a freelancer recovered the prototype. When a spy is caught, scrutiny follows. A decade of operations and actions would be questioned. Saul sponsored the thief's citizenship, but that could be explained. What no Senator wants to explain is a captured spy's role in election fraud.
As a freelancer, Butcher specializes in only one thing. He does it well. He does it efficiently. It also happens to be the one thing a corrupt Senator needs done to avoid explaining what his former employee might reveal.