My son, who is an officer in the RAF, was asked to go to the USA a couple of years ago, in order to give instruction to some USAF officers relating to various things.
He was in a party of 12 officers who flew into Atlanta on a civvy airline and were being picked up by USAF helicopter for onward transmission to their base. On arrival in Atlanta the other 11 sailed through immigration, however, my son was taken away into a room and interrogated because his passport showed that he had been in Afghanistan, Qatar, Saudi Arabia, Russia and various other places were he had served the UK. In spite of his being in charge of the party he was kept for over one hour before the helicopter pilot came in to insist that he was allowed to complete the journey.
HE was advised that, should he wish to go to the USA in future, even though he could be instructing their armed forces, he should obtain a Visa. That was under Biden's lot so I don't think that he will risk this lot.