In "Objections to the Constitution," what does George Mason argue might happen if the president has the power to pardon people?
Mason's concerns about the president's power to pardon should be understood in the context of his objections to the amount of overall power granted to the executive. Mason thought that an executive council should be appointed by the legislative branch, not to advise the president in the way that a cabinet does, but rather to serve as a check on the president's powers. As things stood, he feared that the president might form cabals with other people in government, particularly his advisors, and then pardon them when they committed crimes in association with him.
The President of the United States has the unrestrained power of granting pardon for treason; which may be sometimes exercised to screen from punishment those whom he had secretly instigated to commit the crime, and thereby prevent a discovery of his own guilt.
In other words, the power to pardon would be one more way in which the executive could expand his influence. This was a major theme in eighteenth century Anglo-American political thought, and even though it was not Mason's main objection (he was primarily upset by the lack of a bill of rights and the legal sanctioning of the slave trade,) the fear that the executive would arrogate too many powers to himself permeates his writings, as well as those of Patrick Henry.