How do they tell if you're drink driving in America?

They have to follow due process or take several steps to make sure that they prove that they had a reason to make an arrest. People in america get all upset if they feel like they wernt given a fair chance. They see some one driving weird, they pull them over, ask if the driver has been drinking, if they say yes, they get arrested,if the driver says no but the cop is still suspicious, they give the sobriety test. If they completely bomb the test they are arrested but, people who have been caught before may have learned to pass the minimum mark of the test or if they are just a little bit over the limit they could still walk straight, so if the cop is still suspicious, then they do the breathalyzer. It seems faster to just jump to the breathalyzer but some people are ignorant enough to think that the u.s. Constition some how protects them from the fastest way to catch them doing a crime. It just makes a mess. Some cities fight drunk driving more aggressively than others so not all hope is lost.