Fourth Amendment
When a police officer has a conversation that is at least partially consensual with a person asked to sit in the patrol car while a traffic citation is being written, if the person admits possession of contraband in he first three minutes after the ticket is written, the intrusion is de minimis.
http://media.ca8.uscourts.gov/opndir/16/01/152343P.pdf
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.