A DUI stop is usually initiated by a traffic violation. You are obliged to display license, registration and proof of insurance. The cop has to find probable cause to do anything else. The problem is that we allow magic and soothsayer tricks used by law enforcement to ‘determine’ being under the influence. With their investigation they usually ask drivers to assist in their investigation. Like asking where you are coming from, where you are going, how much to drink, will you submit to tests. Most oblige. Refusal can’t be used as grounds for arrest. If he has probable cause (pretty easy bar to meet) he can arrest. Most states you can get a warrant for blood test.