US Customs still has complete control over port security.
Of course US Customs does not load containers. US Customs Inspectors are supposed to be watching P&Os workers now.
Your suggestion that there will be more for customs agents to watch out for is ridiculous.
No they don't. Port security has various areas, divisions and dimensions. It is shared by the Coast Guard, Customs and the shipping/maritime company that controls the port. That is what P & O has bid nearly 7 billion dollars to do, control the six eastern sea ports involved in the bid.
But if it makes you sleep better at night, then go on believing the nonsensical notion that the Maritime/shipping companies who are paid to control the port entries really have nothing to do with port security. And you can believe in Peter Pan too.