Take, for instance, those guilty pleas extracted from Credit Suisse and BNP Paribas. Last March, Holder said that he feared that prosecuting large financial institutions could hurt the economy. This became known as his “too big to jail” remark — which he quickly disavowed. No wonder he was eager to have some firms plead guilty! Yet, as Peter Henning notes in a New York Times DealBook article, the Justice Department made sure those guilty pleas didn’t inflict too much pain. In the case of BNP Paribas, prosecutors secured agreements from state banking regulators that they wouldn’t pull the bank’s license to do business.

Or take the claim that the Justice Department has been rigorously rooting out mortgage fraud. In fact, after a grand announcement that the department was putting together a mortgage fraud task force, U.S. attorneys around the country began aiming their fire at easy prey: small-time mortgage brokers, or homeowners who had lied on “liar loans.” None of the top executives from any of the major firms were indicted. Indeed, according to an article in The New York Times Magazine in May, only one executive of any kind — a mid-level executive with Credit Suisse — has gone to prison as a result of his actions during the financial crisis. The notion that he’s the only one who committed a crime in the mortgage-crazed run-up to the financial crisis is, quite simply, implausible.

As for those big fines against Bank of America, Citigroup and JPMorgan Chase, not only did they come very late, but their terms were such that it was impossible to know for sure the extent of their wrongdoing. And, of course, despite fines that went into the billions, no actual human was prosecuted for any wrongdoing.

So the question worth asking, as Holder plans to step down, is not what his department did but why it did so little. Why was it so reluctant to pursue the financial crimes connected to the 2008 crisis? One answer is that these are hard cases to prosecute — harder than negotiating a financial settlement with a big bank. Early on, the Justice Department tried two Bear Stearns portfolio managers whose hedge fund — stuffed with mortgage-backed securities — collapsed. The two men were found innocent. That verdict seems to have sent a chill through prosecutors, making them reluctant to go after others.

Jesse Eisinger, the author of that Times Magazine article, wrote that, over the years, the Justice Department saw “an erosion of the department’s actual trial skills,” as well as a drop in resources. In the Southern District of New York, U.S. Attorney Preet Bharara focused — with great success — on insider-trading cases, where he had wiretaps that made prosecutions relatively easy, instead of difficult-to-try financial crisis cases.