The bible isn't mandatory, probably evolved to add to the peoples perception of the person honoring the oath.
It's not like you giving shithead the benefit of the doubt when all his actions have never been by accident.
He's still a crude imbecile with his only salient ideas and plays are for his direct enrichment. Otherwise he doesn't truly care because he believes he really is above all the laws of this country. He has no problem playing golf while his crew with the 2025 book do the heavy lifting. And don't forget, if anything goes down legally, he blames the 2025 book and the shits that are implementing it's plans.