The best place as usual to start is with the part under discussion. From The Constitution for the United States of America, Amendment 6"
It does not matter how minor the type crime ('j' walking, parking, cursing, murder) -- only impartial juries can determine the verdict. No judge can ever render a verdict in any criminal prosecution.
The arresting "officer" must fully inform you of the charges against you and what it is that you have done that brought about the accusation. This means that the officer must have the full text of the law in question --- not merely the code number (with or without it title). Most cases can be won at the side of the road when officers have this information. Many officers are not as knowledgeable about the laws they enforce -- or the jurisdiction within which they patrol.
Since the criminal prosecution begins with the charge or accusation and definitely includes the arrest, Plea Bargains are prohibited. Once the person claims their innocence, offering any plea bargain works to coerce the accused to give testimony against themselves by using threats of harsher penalty if they take it to court and lenient sentences if they save the courts the cost of going to trial.
You literally can have any person you trust with respect to how our courts are supposed to function to help or to advise you of the constitutional process. No lawyer needed.
You also can call any person to be a witness if you can prove they have information that can be used to obtain an innocent verdict. This includes judges and lawyers, police and lawmakers.
The following definitions come from the Samuel L. Johnson dictionary published in 1785: