They only have authority to quarantine sick people who have demonstrated a willful disregard for the health of others (think typhoid Mary). They have zero authority to place the public under house arrest. Bill Barr has authority to use the DOJ to enforce the constitution on any local govt. that disregards the civil liberties of its citizens.
See my prior links...one of them is: https://www.ncsl.org/research/health/state-quarantine-and-isolation-statutes.aspx
2 examples:
Kentucky:
Authority. When the Cabinet for Health and Family Services believes that there is a probability that any infectious or contagious disease will invade this state, it shall take such action and adopt and enforce such rules and regulations as it deems efficient in preventing the introduction or spread of such infectious or contagious disease or diseases within this state, and to accomplish these objects shall establish and strictly maintain quarantine and isolation at such places as it deems proper.
Louisiana:
Authority. The state health officer has exclusive authority to isolate or quarantine to prevent the spread of contagious disease. If a parish becomes infected with a disease to the degree that it threatens to spread to another parish, the state health officer can quarantine that parish. Parish health officers may establish quarantine only with permission of the state health officer and parish legislative body, and shall be supervised by the state health officer.
Sounds more like “general isolation” to me for those 2 states (and others)...Barr would have a case if everyone in a state was tested in a short time frame, and everyone that tested positive was quarantined immediately away from the negatives and kept there until testing negative (recovered). Then you could release all the negatives to do whatever they wanted & re-open all the businesses and start gatherings again. This kind of widespread testing has not happened yet.
I am for stopping the SIPs and re-opening businesses by May 1 (”Flattening the curve” accomplished), but like I said before state and county health depts. have priority over the Feds by law and court precedent.