The answer is; it depends, both on your vista status and the type of experience you are completing in the United States.
For example, a for-credit rotation (the categories of which are defined here) allows students to have expanded responsibilities with their school’s guidance, which must be reflected in the Letter of Enrollment (LOE) and the conversation during your border crossing. For-credit clinicals have a more limited inventory, are offered in fewer states than “Not for Credit”, are under more strict supervisory policies by the U.S. Department of State, and various medical boards (since a for-credit clinical elective may involve the student practicing to be a doctor, also known as practicing limited medicine without a license). Visiting students signing up for this type of rotation should ask for a letter of sponsorship from their medical school documenting as much details and their approval of all clinical elective(s) taking place in the United States, and that they are in good standing with that medical school.
For rotations that are not for credit, it means that your medical school has no involvement in this rotation as this is not a part of your curriculum, is being done during your vacation time (not during the regular semester) and thus is categorized as a volunteer activity. In this type of rotation, you must not portray yourself as a medical student doing for-credit clinicals (i.e. introducing yourself as a 3rd or 4th or 5th year medical student, or sharing your diagnostic opinions, etc.) Not for credit type of CB is not work, unpaid, and will not go on your transcript, therefore most state medical boards do not govern this type of experience, and do not care if your medical school is approved in that state. This also means you are coming to the U.S. to watch medicine be practiced (and not be the one who practices medicine, such as limited practice by medical students from properly processed and pre-approved medical students in for-credit clinicals), therefore categorized by the Department of State (U.S. border control and embassies) as observational. If this is the type of clinical rotations you are signed up for, then make sure that you do not confuse the border patrol officers by telling them you are coming to do clinical electives, as that would be a misrepresentation of your medical school’s involvement.
You are required to immediately disclose the for-credit or not-for-credit status of clinical rotations with AmeriClerkships prior to enrollment, by way of completing the AmeriClerkships Clinical Authorization Letter.