Crap like this won't stop until there are large lawsuits with financial penalties for thse types of opinion based actions.
This crap is just wrong.
The first lady got stopped during "amateur hour", the hour around closing time. It is the worst time to travel, not just because of the late-night bar closing crowd, but because police are out in force looking for those high dollar tickets. If you work at a bar, you are a target, too, by virtue of where you are leaving, and the time you leave.
For a policeman to assert he thinks you have been smoking pot, though, he should have to smell pot in the vehicle (where the smell can persist for a long time) or on your person (worse than cigarette smoke, imho) or find evidence of drugs or paraphernalia on you or in the vehicle. Without that, the assertion is merely one of opinion and without evidence. That does not mean the officer will not lie.
If screening tests can be conducted in 20 minutes (for eight drugs/classes of drugs) with a urine kit from Walmart, there is no excuse for not allowing exculpatory evidence to be produced promptly and letting the person go. I would think the courts would rule the same if suit was brought. The person has already proven they are not guilty of driving under the influence of alcohol.
Unfortunately many states have laws on the books which allow you to be arrested and possibly even convicted of 'drunk' driving or 'impaired' driving without testing above the limit, too. Know the laws in your state, and softly remind the officer that you do know the law, and are not in violation of it.
If you can't do the field sobriety test to the satisfaction of the officer (Hold your left foot 3.5 inches above the pavement in a high and gusting crosswind at 20 below and recite the passenger list from the Titanic in reverse alphabetical order starting with the M's...) you can be arrested and the subjective charge will probably stick, even if your BAC is below the legal limit.
Unfortunately, with all the different intoxicants out there, and no reliable test or levels of intoxication established for most drugs, red eyes, a long day, and bad roadside conditions (and a cop short on quota) can lead to a life changing event if you are not permitted to take a test which shows you are 'clean'.
As a preventative measure, it pays to make sure your headlights are on (at night in town), that all lights on the vehicle are functioning (including license plate lights), and that you signal appropriately, for starters. That removes many of the excuses for pulling you over. If the stop doesn't happen, the paperwork doesn't happen, you sleep in your own bed.
Traveling, when possible, before the herd, (going home with off-sale) can get a person where they are going without complications, because it isn't DUI rush hour, and your transit will be treated much the same as any other vehicle going from point A to point B.