How do you know? If it was EVER true, it has NOT been true during your lifetime. If you believe so, name the POTUS and I will educate you on his scandals.
I was born in 1946, one of the original Boomers. You do note that I said "be publicly held to the highest standards of dignity and probity." By that metric, most of the President's in my lifetime qualify. I did not say scandal free..and most weren't..although you'd be hard pressed to find a lot of dirt on Ike..other than his affair with his driver during WWII. Decidedly NOT public. Ford had some issues with
gravitas..but he had the guts to pardon Nixon at the cost of his political career. BTW, I would have done the same with Trump and put it all to bed. Not up to me.
Clinton was not so dignified either..and he certainly took his scandals public. It scarred his Presidency..and may well have paved the way for a Trump.
Kennedy had all his linen in the public eye..and most did not care, at the time. He still adhered to certain public standards.
Obama embodied Presidential dignity. Calm and reasoned. Some on the left think that that cost him.
Both Bushes, evil fux that they were, stayed dignified in public.
You see, everyone has dirty laundry..and you can pull out some scandals on any one of the Presidents. Trump was the first though, to brag about grabbing pussy..and get elected anyway.He liked hanging out in locker rooms...of teen-age beauty contestants. He publicly flouted afairs..in the face of his wives. He was the first to ally himself with the bottom-feeders of the country, to lie baldfaced, and double down on false statements. He openly calls Democrats communists...and your ilk cheer him on. He trolls for loose change at every opportunity, indulges in questionable, at best, business practices. He casts doubt on our institutions, on our elections, and refuses to do the right thing--no matter what.
He has no dignity..and those who have gone down the rabbit hole with him even less.