Perjury is perjury
Shortly after the bit you quote, Todd observed that in a he-said/she-said situation (the example being Trump's word against Comey's), a person's record for truthfulness can resolve the matter. And Rudy just ignored him. You know truth has entered the room when Rudy shuts his mouth.
You can't shield a pathological liar from committing perjury, any more than the scorpion can keep from stinging the frog as they cross the river. Trump has to be true to himself.