May a President joke about the power of the presidency?

Glenn Reynolds says no — at least when it's Barack Obama threatening to sic the IRS on somebody that crosses him.

Surely he's aware that other presidents, most notably Richard Nixon, have abused the power of the Internal Revenue Service to harass their political opponents. But that abuse generated a powerful backlash and with good reason. Should the IRS come to be seen as just a bunch of enforcers for whoever is in political power, the result would be an enormous loss of legitimacy for the tax system.

Glenn's being practical and focused on the special problem of our income tax system, which depends so heavily on self-reporting and compliance. He's not talking more generally about the requirement that Presidents be ever serious about their awesome powers. So don't be like bad Mr. Nixon. But, presumably, this is still okay: