There's a new and provocative working paper suggesting that the president's recess appointments power is more limited in scope than the prevailing practice. A professor at the University of San Diego School of Law suggests that the president has only the power to make recess appointments for vacancies that arise during the recess, not any vacancy that arises before a recess and happens to continue during the recess. He also suggests that the Recess Appointments Clause only permits the president to fill vacant federal offices during the intersession recess, not the brief intrasession breaks. Michael B. Rappaport, "The Original Meaning of the Recess Appointments Clause," unpublished working paper (download the abstract or full paper).