Speculation was that he was a ‘registered Republican’ so that he could vote against Trump in the primary.
Which makes sense from what we KNOW happened in the primaries running up to 2020 national. Yes— lots of quickie crossovers paid to vote that way and in the national. See: Philly voter fraud hearings with Giuliani (videos hours long with the blond wigged councilwomen sneering “we ain’t messsin’ wid-jouuu” black ostensible woman).