A constitutional system of checks and balances is premised on the assumption that government officials will seek to get as much power as they can. Constraint itself becomes a dirty word. Admittedly, the desire to resist or ignore constraints may be in human nature itself, though people differ in how much self-discipline they will bring to the task of restraining themselves from walking through constraints as if they were Chinese walls made out of paper. A constitutional system that checks ambition with ambition must not assume that some of the more beloved elected representatives can be relied on to resist the temptation to go too far. I have in mind the case of the U.S. president being able appoint officials without the confirmation by the U.S. Senate.
The full essay is at "Presidents Buck Constraints."