A portfolio of that size gives the comptroller a potentially far-reaching perch from which to watch over Wall Street. The funds are large shareholders and customers for Wall Street. It won't be hard for Spitzer, if he were elected comptroller, to find a reason to poke around on anything he wants. Hedge funds, private equity funds and investment advisory firms will scramble for a piece of that $140 billion. Spitzer could become one of the most powerful activist investors on Earth.
Spitzer has been dropping hints that he has big plans for the office, telling The Wall Street Journal that "the office, like the attorney general's office before he inhabited it, has underutilized potential."
(Read more: Eliot Spitzer's Favorite Hooker is Now a Commodities Trader)
(Disclaimers: At some point, Spitzer worked for Skadden, Arps, Slate, Meagher & Flom, which also employed me after law school; we never worked there at the same time. One of my law school classmates, city councilman Dan Garodnick, had been campaigning for comptroller's office but dropped out of the race last November. I think I may have once attended a $20 fundraiser for Garodnick back when I was practicing law. I have close friends who have played various roles in campaigns for Scott Stringer, another Democrat running for the comptroller's office. I once met Ashley Dupre, the woman involved in the prostitution scandal, at a party in the Hamptons. When Spitzer resigned, I organized a tongue-in-cheek send-off party for him at a bar called Spitzer's Corner; he did not attend.)
—By CNBC's John Carney. Follow me on Twitter