Why are Giuliani and Barr promoting the notion of absolute immunity for the POTUS? Because, as a result of an historical oversight, it is a privilege prosecutors at all levels still enjoy and there is an interest in “fixing” the principle in the law for good. In a sense, Trump’s claimed immunity from being accountable to the law is comparable to the kerfuffle over Hillary Clinton’s emails, which wasn’t about Clinton, either. In the latter case, Capitol Hill was actually keen to set a precendent that would support legislators’ electronic communications should be exempt from record-keeping requirements. In the case of absolute immunity, prosecutors are concerned that their exemption from judicial review is about to be removed, either by SCOTUS or the Congress.
Ulterior motives are the stuff of which the instinct-driven are made. Makes sense. If crime is a matter of intent, then shouldn’t people who don’t think get off scott free? On the other hand, didn’t the framers of the Constitution hedge their bet (that the natural person is moral) by insisting that public servants take an oath?