At the time he was one of the very top lawyers in the country and would have been a first choice if you could afford him. FDR tapped him for what became the OSS for many reasons but a prime reason was his already well established connections to the Brits. By all accounts Donovan was a man that we could really use today but the establishment would be scared silly of him, he had morals!
A new book names Donovan as involved in the conspiracy to kill Patton. Haven’t read the book, don’t know how credible it is, but the death is definitely suspicious.