Why did patrick henry feel that a king would be preferable to a president under the new constitution?

Patrick Henry along with many others saw very little difference between a King and a President. There had never been a President. They were suspicious of the idea because "what could stop him from becoming a dictator?" They had experiences with a king and understood the basics about using a Parliament or some form of legislative body to keep a king under control. There appeared to be nothing like that in the new government.