One of the standard tricks of the trial lawyer litigating against a corporation is to cherry-pick a single email or memo, and attribute its information to the collective knowledge of the corporation. Years later, with 20/20-hindsight, trial lawyers tell a jury that the top executives and decision-makers should have known about the napkin-scribblings and stray emails of the mid-level engineers.
This is a naive (or disingenuous) way of understanding how corporations, or any other bureaucracy, work. Organizations are made out of individual people, and knowledge gets transmitted up or down the chain inconsistently. The government, and the Department of Justice, is certainly no different. Hundreds of thousands of decisions are delegated by statutory law to the attorney general, who necessarily delegates them down the chain to lower-level attorneys. Lots of attorneys and staffers are writing memos about the hundreds of thousands of cases and programs in dozens of different divisions in the Department of Justice, and these are filtered up the ladder by intermediate staffers and attorneys, and the attorney general is hearing about a small fraction of them. So it's entirely plausible when Eric Holder says that he did not know about the ludicrously irresponsible "Fast and Furious" program, a horrific example of governmental incompetence that provided guns to Mexican drug cartels in the hopes of generating some prosecutions of legitimate gun sellers in the United States. It's too easy to confuse the accusation "Holder received information and updates" with the more conservative and precise statement "there was a memo addressed to Eric Holder." The latter is true, but it doesn't necessarily mean the former is true.
Threatening elected officials with a perjury trap using this sort of abusive tactic is not just bad policy (the politics of personal destruction is a way to reduce the number of qualified individuals who go into government), but it's bad politics for Republicans. These cases are prosecuted in the District of Columbia, and it's much harder for a Republican facing perjury charges on this sort of attenuated claim to get a fair jury trial than a Democrat: just ask Scooter Libby. And at the end of the day, the Left has more targets to use this sort of unfair tactic against than the Right does.
Now, whether Eric Holder should be taking more responsibility for Fast and Furious is different than whether he should be criminally prosecuted for it. As the late Steve Jobs once said, that's the difference between a janitor and a vice president:
One such lesson could be called the "Difference Between the Janitor and the Vice President," and it's a sermon Jobs delivers every time an executive reaches the VP level. Jobs imagines his garbage regularly not being emptied in his office, and when he asks the janitor why, he gets an excuse: The locks have been changed, and the janitor doesn't have a key. This is an acceptable excuse coming from someone who empties trash bins for a living. The janitor gets to explain why something went wrong. Senior people do not. "When you're the janitor," Jobs has repeatedly told incoming VPs, "reasons matter." He continues: "Somewhere between the janitor and the CEO, reasons stop mattering." That "Rubicon," he has said, "is crossed when you become a VP."