There are three ways the State can charge anyone with driving while intoxicated: per se (a breath alcohol content of .08), impaired by the slightest degree (impaired due to the consumption of alcohol to that point that you can not operate a vehicle safely), and impairment due to ingesting drugs.
In a recent trial, I had the honor of representing a gentleman who was charged with driving while under the influence of alcohol and the state brought two theories of intoxication: per se (.08 breath alcohol content), and impairment to the slightest degree.
The investigating officer testified that my client was so drunk, he couldn't even stand up straight during the instructions portion of the field sobriety testing. He said the instructional phase of the testing took about 20 seconds and my client was supposed to stand straight with one foot ahead of the other. According to the officer, my client almost fell several times and had to throw up his arms to use them as a de facto balancing pole just to stay standing for the 20 seconds. Wow!
Then, I got the officer to admit that he had my client walk across the street about 100 feet to a well-lit parking lot to conduct the field sobriety tests, walking to the parking lot took about twenty seconds, and my client was able to walk just fine to the field sobriety testing area (he never needed to throw up his arms to use them as de facto balancing poles to keep his balance). I also got him to admit that my client's driving was fine, that in order to drive a motor vehicle, you don't ever have to stand straight with one foot ahead of the other, etc., etc.
Needless to say, by the end of my cross-examination, it was clear that the jury would acquit my client of driving while intoxicated (impaired to the slightest degree) --and they did. DWI is a very fact-specific crime. Often, there are many defenses available in the cases.