... which brings us to the reason why the D'Souza persecution theory will stick: to its believers, it doesn't matter whether he did it or not.
(Story about conservative responses to the indictment of Dinesh D'Souza for violating campaign finance rules)
That is one way of putting it, with the obvious implication that the believers are wrong.
Another is to observe that, according to one recent book, our legal rules have become so complicated that the average American commits several felonies, at least arguable felonies, every day. If that is anywhere close to true, a political faction with control over criminal prosecution could punish its opponents—D'Souza is, among other things, the producer of a film critical of President Obama—without ever prosecuting the innocent, there being few innocents to prosecute.
As long as more illegal acts are committed than are prosecuted, surely the case in any real world legal system, selective prosecution can be an effective tool for suppressing activities those in power disapprove of. Back during prohibition, prosecutors who were unable to convict mobsters of murdering people or selling illegal liquor got them for income tax evasion instead. I have no data, but I suspect there were a lot of other people evading income taxes who attracted less prosecutorial attention.
All of which ties into the recent NSA controversies in two different ways.
We have the case of the director of national intelligence, who, having by his own admission lied under oath in his congressional testimony, is not being prosecuted for perjury. That is a case not of one political party against another but of a government protecting someone who committed a crime the government approves of.
It seems clear that the metadata being collected from the phone companies is accessed by law enforcement—the DEA, probably the FBI, perhaps others—as well as by the NSA. Analysis of that data—what number called what number when, for essentially all phones in the U.S.—is likely to reveal a good deal of information about what people are doing. Law enforcers with access to that information and their own view of who does or does not deserve punishment could use it to discover illegal acts and prosecute them or to discover acts that are legal but disreputable and leak the information to friendly news media; the pattern of who called whom when might, for example, reveal the marital infidelity of a politician. The ability to expose the crimes and sins of your political opponents and only your opponents could be very useful to any party in power.
How could one structure a legal system to avoid that danger? One answer is by making criminal prosecution private, in effect expanding tort law to swallow criminal law, an idea I have discussed from time to time under the title "Should We Abolish the Criminal Law?" A video of one such talk, delivered in Warsaw, is webbed here, a more recent one, delivered in Berkeley, here.
Of course, the problem would still exist if the private prosecutors on one side had access to better information, telephone metadata, say, than the other. Which is one reason to sharply reduce the ability of government agents to get such information.