Getting my Thai kids a Tourist visa for USA

I had a disappointing week. I am a US citizen, with a home in Hawaii and one in Bangkok. I am married to a Thai, who has three grown up children from a previous marriage. I adopted the three kids here in Thailand. I wanted to invite the kids (who are all in their 20's and are college educated and self employed) for a summer holiday to Hawaii. I helped them apply for tourist visas with the US embassy, paid over 5,000 baht per person for the process, and when they went this week to the embassy for their interview, they were rejected, without even having an opportunity to present my invitation letter and their support documents to the nasty Consular office who "interviewed" them. She asked them one or two questions and then handed them a rejection letter, without even giving them a reason for being rejected. I find this outrageous and highly disrespectful to me as their adopted father and being a US citizen. My question is: does anyone here have a similar experience and can offer me advice on a successful method or strategy for these kids to re-apply for tourist visas? Or is the xenophobic Trump administration making it almost impossible for "normal" Thais to get tourist visas? Your feedback, please.