I think it is testing to see how much they can get away with

'Cause this keeps happening. 

As far as I can tell, the feds are either hiring totally incompetent people to run these checkpoints or they are testing to see how many people can be herded sheeplike into giving DNA sample and even blood samples because the "checkpoint" is manned by people dressed like and acting like policement, and because "real" police are directing traffic.

Yes, I am sure that they told each and every person diverted into the checkpoint that the stop and subsequent sampling was "voluntary". I bet that there were signs and such making sure that everyone knew that there was no issue of you refused....

Is it? Are most people going to think it is voluntary when a person wearing a uniform asks you in an intimidating manner to open your mouth and takes a cheek swab? Or in a stern manner tells you that they are going to take a blood sample?

Yeah, you and I might not be willing to give up such samples, but Joe the "low informatin voter" might not be sure that he CAN refuse without being arrested...and Suzy Homemaker will likely be too afraid to resist, even if she is aware that there is no legal reason for the search.

Two things if this happens to you:

"warrant"

"am I free to go now?" 

followed by:

"Lawyer".