Proponents of the “unitary executive” theory hold that “all federal officers exercising executive power must be subject to the direct control of the President.”  But how, as a constitutional matter, should such presidential control be defined, and how should it be effectuated?  Unitarians are not united.  Kevin H. Rhodes and Professor Steven G. Calabresi identify at least three distinct versions of the theory, which reflect a diversity of responses to those questions.  The strongest or most aggressive version (which may also find the least support in the relevant jurisprudence) holds that the President may “supplant any discretionary executive action taken by a subordinate with which he disagrees, notwithstanding any statute that attempts to vest discretionary executive power only in the subordinate.”  In other words, Congress may have assigned a specific task or decision to another official, but the President is constitutionally empowered to substitute their own judgment for the subordinate’s.  A weaker version holds that the President may not supplant another official, but that they may “nullify or veto [the subordinate official’s] exercises of discretionary power.”  The President cannot act in the subordinate’s place, but the President can require the subordinate to reconsider their positions.  A third version, which appears to be the most modest, at least as a formal matter, holds “that the President has unlimited power to remove at will any principal officers (and perhaps certain inferior officers) who exercise executive power.”  In other words, the President can neither nullify their subordinates’ decisions nor substitute their judgment for that of their subordinate; but at least with respect to those the President appoints, the President can replace them with others until they find someone willing to do their bidding.  This version may seem to be the most modest because the President’s formal power is purely remedial (and does not itself undo any decision already made), but it may well be the most potent as a practical matter.  Indeed, the removal power is often considered a proxy for actual supervision and control, based on the assumption that most executive branch officials will ordinarily choose to follow the President’s wishes rather than risk forfeiting their positions, without regard to whatever degree of independent decision-making authority Congress has given to them.