Failure to convict the same person several times in a row on essentially the same charges is considered prima facie evidence of government misconduct, especially when the charges must be brought about by undercover sting operations.
We are not talking about randomly picking people to prosecute here but those who the government reasonably believes are hiring illegals.
The only way they're going to find a significant number--i.e., enough to deter others--is to engage in undercover stings. And at that point, you have the government soliciting criminal activity. That's what Reno's effort--the one you wish to duplicate--did.
And if you think that multiple charges against a defendant equals a harassment suit, there would never be trials of organized crime figures as they have been known to beat the charges.
Key difference: the government did not actively solicit the targets of these investigations to commit crimes. To generate criminal charges against enough employers to act as an effective deterrent, you're going to have to manufacture the cases in the same fashion that many drug cases are manufactured today.
The intersection of failed prosecutions and said prosecutions being based on undercover sting operations is very much frowned upon by the judiciary.
And finally, this is all assuming that you're right that juries were just rarin to nullify on illegal immigration cases. You rely first on supposed twenty year old cases that you cannot cite. Now, you point to polls that have not been taken.
Not every opinion poll is publicized for your edification, sir. Indeed, most are not disseminated to the public.