Most arrests for drug offenses do not arise from a carefully planned surveillance operation where police have sought warrants to place GPS trackers on vehicles, or collected trash outside the residence to go through later at the police station. In fact, most drug offenses emerge from routine traffic stops—speeding, no seat belt, failing to signal a turn, and the like–that ultimately lead to the discovery of drugs somewhere inside the car.
Minor traffic offense like the above are sufficient grounds for a traffic stop (a temporary detention.) Troublesomely, even a cop’s mistake about the law does invalidate a temporary detention, so long as the mistake is reasonable. (For more on this, see: https://georgeroland.com/cops-can-be-mistakenyou-cant-part-i/ and https://georgeroland.com/cops-can-be-mistakenyou-cant-pt-ii/ )
After the officer has pulled the driver over, the officer can investigate the traffic offense—meaning the officer is permitted time to briefly discuss the offense, and issue a warning or ticket, and then release the driver. However, if during the investigation of the traffic offense, the officer notices, say, the smell of marijuana or sees drug paraphernalia in plain view, the officer now has reasonable suspicion to investigate drug activity—not merely a traffic offense. To be clear, the cop doesn’t have to smell pot or see a bong in the car: if the driver is nervous, makes inconsistent statements, and has prior drug arrest, this can also provide reasonable suspicion to investigate drug activity beyond the initial traffic offense.
And from here it’s off to the races.
Suppose the officer now wants to search the driver’s car. If the officer smells pot (whether he or she really does, or simply says he or she does), the officer can conduct a probable cause search of the car. If the cop doesn’t smell pot (and doesn’t feel inclined to say he or she does regardless), the cop always has the option to arrest for the minor traffic offense (with the only exceptions being for speeding and open container) and then conduct an “inventory search” of the vehicle. Under an inventory search, police go through the vehicle under the auspices of making a list of the vehicle’s contents to protect the police from claims of theft or vandalism. (In essence, to prevent the arrested driver from claiming he or she had $1,000 in cash in the glove box when arrested, which is now missing after the car is retrieved from impound.) In practice, the “inventory search” is very much like the “community caretaking” doctrine (See: https://georgeroland.com/shame-on-the-state-part-ii-why-the-community-caretaking-function-is-the-biggest-threat-to-our-fourth-amendment-rights/ ), insofar as both are ripe for abuse and seem to be abused routinely.
Because justifications to search a vehicle that has been stopped are numerous and heavily favor giving police the benefit of the doubt, the stop itself provides a better target for challenge. Absent reasonable suspicion, police have no authority to conduct an investigatory stop/temporary detention. If an unlawful stop led to the discovery of drugs, that evidence must be suppressed (tossed out.) (See: https://georgeroland.com/drug-charge-stops/ )