The cop will have one more piece of evidence to arrest you on. No dwi is made solely on you failing a single test, the judge would laugh their ass off for that. But when you tell one, “he was swerving across multiple lanes, smelled of alcoholic beverages, couldn’t say the alphabet starting at e and ending at t, had XXX nystagmus (there’s like three types they check for), did PZY clues on the walk and turn test, and admitted he had been at the bar an ‘hour or so ago,’” they suddenly have a very different conception of what failing to remember the alphabet means.

Remember, don’t answer any questions on a traffic stop, kiddos. It’s always shut the fuck up friday. ALSO, fuck people who drive drunk, but mostly don’t give cops the time of day if they ask, much less any other info.

I still don’t get why the US sobriety tests are admissible by a judge. cops can just run a breathalyser test (or even a drug test), it’s faster than all these weird test and more reliable.

If your going to arrest someone anyway , you can even get a blood/urine sample for a lab-grade drug search.

The blood/urine/breath samples come AFTER the arrest. At least where I live, blood needs a warrant, which they aren’t getting without enough ‘evidence’ to convince a judge. Hence the roadside sobriety tests. They can take a breath sample because the law requires that you give one if you have a driver’s license (it’s part of all the legal paperwork you sign when you get one), but you can’t really force someone to give a breath sample because it’s not a simple thing.

The breathalyzer and blood are definitive tests, but they aren’t needed for the arrest or the conviction. A cop that I know said the best cases were the ones where he stood a driver in front of his car’s camera for about five seconds and you can see them visibly fall over or stumble while just trying to stand there. Criminal cases are always about convincing a jury, and that means that ‘evidence’ like a car swerving on the highway, the smell of alcoholic beverages, the field sobriety tests, the general appearance or manner of the driver, the statements made, etc., all matter.

It depends on the state; you aren’t required to take a breathalyzer in all states, nor are your required to submit to field sobriety tests in all states, although refusal can have different results depending on the state. It would be best to check the laws in your state. source
The Ultimate Guide to Breathalyzer Tests in the U.S. [US Law Explained]

According to the link you provided, every US state has implied consent laws which trigger an automatic DL suspension if you refuse a breathalyzer.