When I was on my way to the pub with a few friends, including one who was a police officer, he spotted a drunk heading towards the car park and followed him, but he didn’t pounce until he saw the guy putting the key into the ignition before arresting him for being drunk in charge of a motor car, otherwise the guy could just have claimed he was going in to sleep it off rather than had an intention to drive drunk.
a person
operating a motor vehicle on a public street of highway
while intoxicated
Those are the elements of a DWI in Texas.
If you are not driving the car, can’t be arrested and charged with a DWI.
In the UK, a few years back, I was riding with a police officer in Lincolnshire, he saw a car that was blocking one of the narrow ally’s.
He took out some tools, opened the car, moved to clear it and then re-locked it. Nice.
But when he opened the car the discovered marijuana bags below the drivers seat, so he arrested the missing driver.
No 4th amendment protections, searching without probable cause but didn’t matter there.