[ARCHIVE ANSWER]
A past arrest for drugs is another "reasonable suspicion" but not "probable cause for search." A citizen's criminal history is an indicator of his willingness to obey/break certain laws. The National Crime Intelligence Center (NCIC) is at the fingertips of all law enforcement and keeps arrest/conviction data of all citizens.
Most people think if they were not convicted, the arrest does not show on their record.
Not true. A criminal history generated from NCIC reports the number of arrests and whether the arrest ended in a conviction or not. Just an arrest gives a citizen a criminal history.
When learning of a citizen’s criminal history, police never consider whether the crime was successfully prosecuted. The arrest alone is enough to give them another "reasonable suspicion." Unless the officer personally knows you, a criminal history can only be accessed by knowing a person's name/date of birth/social security number/driver's license number or any combination. You must be pulled over and stopped to give this type of info. Police cannot run your license plate and gain enough info to run your criminal history.