Coming back on UA from MEX to IAD, they did a complete manual search of our checked and carry-on baggage, along with an ID check, another ID check at the metal detectors at security, then they did a complete second manual search of our carry-ons at the gate (for everyone), then they wanded us manually for metal and another ID check before boarding.
It was a complete contrast to going from IAD to MEX which was much more casual.