https://www.techdirt.com/articles/20200119/11281443762/court-tosses-evidence-pretextual-stop-when-dashcam-shows-cop-had-zero-reason-to-perform-stop.shtml

The #BacktheBlue types like to say stuff like "If you don't want to get arrested, don't break the law." But breaking the law is never a prerequisite for a traffic stop, search, and/or arrest. The nation's top court has already said cops don't actually have to enforce real laws. They can predicate stops on what they perceive the law to be, whether or not any actual law was broken.

Pretextual stops have also been given the Court's blessing. As long as there's a good enough reason to initiate a stop, cops can begin fishing for info or consent for a search. But they have to be quick about it and they have to have something approximating reasonable suspicion to continue questioning unrelated to the stop. There's not enough of a bright line drawn anywhere that would ensure success in a lawsuit or a suppression hearing. Cops know this so they play the odds.