Final answer:
John is mistaken about the need for probable cause or a warrant for border searches. Customs and border protection agents can perform searches at the Mexico-U.S. border without a warrant due to the border search exception.
Step-by-step explanation:
Searches at the U.S. Border
When it comes to border security and law enforcement, the standard legal procedures that require a warrant for searches do not always apply. At the Mexico-U.S. border, for instance, customs and border protection agents are granted additional authority to perform routine searches without a warrant. This falls under the border search exception, which is a recognized exception to the Fourth Amendment's probable cause and warrant requirement. Therefore, John is incorrect in assuming that as long as everything is working on the car, the Border Patrol will have no probable cause to stop and search them without a warrant. This exception specifically allows for the search of vehicles and personal belongings at international borders and their functional equivalents without the need for a warrant or suspicion.