@UncleMark You might also be interested to know that the Rules of Professional Conduct have special conflict of interest rules for government lawyers. In short, they allow government lawyers to move to private firms that include clients they may have previously been adverse to, so long as they don't divulge any government confidential information, and the firm insulates them from any future representation.
(The lawyers on here might cringe and say it's more complicated than that, but I'm just giving the broad strokes.)
The general purpose behind the special rules is that we don't want to discourage qualified lawyers from public service, which is what would happen if the ethics implications of government work were too onerous.