What should a patent attorney/agent do if a material prior art reference is discovered after a U.S. patent has issued?

If a material reference comes to the practitioner’s attention after the patent has issued, the practitioner needs to have a discussion with their client about what this means to their patent. The client then needs to make the determination, with advice from the practitioner, as to whether they should file for reexamination or supplemental examination because without one of those, the client may have an invalid patent that otherwise could be fixed.