Mr. Madison thought it indispensable that some provision should be made for defending the Community agst the incapacity, negligence or perfidy of the chief Magistrate. The limitation of the period of his service, was not a sufficient security. He might lose his capacity after his appointment. He might pervert his administration into a scheme of peculation or oppression. He might betray his trust to foreign powers. The case of the Executive Magistracy was very distinguishable, from that of the Legislature or of any other public body, holding offices of limited duration. It could not be presumed that all or even a majority of the members of an Assembly would either lose their capacity for discharging, or be bribed to betray, their trust. Besides the restraints of their personal integrity & honor, the difficulty of acting in concert for purposes of corruption was a security to the public. And if one or a few members only should be seduced, the soundness of the remaining members, would maintain the integrity and fidelity of the body. In the case of the Executive Magistracy which was to be administered by a single man, loss of capacity or corruption was more within the compass of probable events, and either of them might be fatal to the Republic.
Italics are mine.