Slate pre-empted me - sort of. The discussion of what can and cannot be done to Michael Nifong, the odious prosecutor who apparently likes bringing charges against obviously innocent people in order to win elections, involves a lot of legal principles - executive discretion and sovereign immunity being important ones. The author of the article examines it in a very focused way, leaving out two vital parts of the analysis - but then, the article doesn't pretend to be anything other than a discussion of Nifong's criminal liability. I don't know the law well enough to know whether Nifong had to have been knowingly violating a constitutional right - if the conduct was only ambiguously violative, he's not liable under 42 U.S.C. 1983 - or whether the criminal statute has other standards.
42 U.S.C. 1983 is one of the important things missed. It provides for damages against anyone violating civil rights under color of law. Now, for the lacrosse players, money may be more satisfying than getting Nifong convicted, unless they really want to humiliate him. I wouldn't blame them. But he has to have known that the right he was violating was settled constitutionally, which might be hard to prove. He could argue that he was merely being a shrewd prosecutor.
The other problem is that federal prosecutors simply have no good reason to prosecute a state DA and lots of reason to refrain from it. Besides the federalism issue (can the feds dictate the terms of state prosecutions to such an extent that they actually fine/jail people?), there is a natural reluctance for courts to get involved with the executive (except the Supreme Court these days). So-called "political questions" are issues where someone in government has done something wrong, but the proper remedy is not judicial. The remedy in those cases is an appeal to the common sense of the electorate, who will "vote the rascals out of office," as my Con Law professor says. In this case, Nifong was re-elected.
Federalism and judicial restraint seem to lose their force in the face of stupid voters. See 2006 elections.