It’s not easy for an untrained eye to distinguish between a commercial CD, a closed CD-R, and a CD-RW.
All computers these days have USB - otherwise the keyboard and mouse don’t work. You probably can’t even buy a computer these days that doesn’t have USB. Nearly all computers come with DVD/CD writers. Read-only CD or DVD is about 10-year-old technology.
There were plans to prevent this sort of thing, but one important part of the plan was some level of trust in the process of granting a security clearance to a given individual.
We live in an era when our country's laws are disregarded. Yes, they are disregarded by those who are in charge of carrying out the laws. Men can come to a polling place with sticks intimidating voters, people can voter mulitple times and vote when inelligible, enter the country and stay illegally and then get tuition discounts at colleges and free public schools and health care. There is no legal penalty for disobeying our laws. In fact, because our country may have done this, that or the other to this group or that, to enforce our laws is now deemed racist.
Likewise, apparently those in the current administration view the leaks as part of the transparency process and so far have refused to aggressively stop or at least go after those who would like to maximize the damage to U.S. security by releasing damaging cables piecemeal.
How much more damage can the current administration do, by its actions and inactions?