His argument seems to be that no other former President has ever been prosecuted, because immunity from criminal prosecution has always been a part of Constitutional design, And they didn’t commit horrific crimes because they might be prosecuted, which is still true.
Or maybe there were also other reasons that they mostly (not entirely) didn't commit crimes while in office because they thought committing crimes was a bad thing to do? Wouldn't look good for them or the country? Maybe?
Also, lots of things that 'no other' has done are what tfg has already done.
To be slightly more fair, he did say they “would be immediately impeached and removed from office,” not prosecuted, but that seems a little hollow as Trump’s own party refused to convict him for trying to overthrow the government.