My brother was turned back when he flew to Miami with his family to take his children to Disney World.
It turned out that because he had been arrested aged 19 and failed to declare it that the border people felt that he had answered fraudulantly when challenged on "Have you ever been arrested?".
My brother answered no because whilst he was arrested he was never charged or convicted. He had attended a demonstration in the North of England and when a few people caused trouble the police had just arrested everyone only to release the vast majority some hours later.
He'd forgotten about this because nothing had ever actually come of it and it was over 20 years ago, yet there he was being confronted by it at a US border.
Clearly the UK authorities already share data with the USA on its citizens, even those never charged or convicted.
That it may happen more does not surprise me the least. The only part that surprises me is that the data flow might go the other way too.