Due to the invasiveness of the procedure, I don’t imagine the current administration would find much use for it.

Or: "All Liberals must undergo an American Loyalty Test. Your thoughts will be observed and if any anti-american sentiment is discovered you will be deported!"

If it's used against an "enemy" group the invasiveness (potential pain) would be viewed as a benefit to them.

Not that I think this could be reasonably carried out in a country of 400 million people, but I wouldn't for one second doubt their willingness to try eventually.