Opinio Juris has this interesting post by Kevin Jon Heller on the Presidential power of Pardons.
I’ll just add that case law supports that the President has near plenary powers of clemency. The Supreme Court in both Ex parte Garland, 71 U.S. (4 Wall.) 333 (1866), and more recently Schick v. Reed, 419 U.S. 256 (1974), has affirmed that the President’s powers have no limits. In Garland, the Court noted that the “power of the President is not subject to legislative control.” And in Schick, the Court held that because the clemency/pardon powers flow directly from the Constitution, the power “cannot be modified, abridged, or diminished by the Congress,” and the President may even replace the sentence adjudged by another legislatively-created sentence.
For a more in-depth discussion, Shephardize either of the above two cases or, alternatively, read the very good House of Representatives, Committe on the Judiciary, Subcommittee on the Constitution (we’re getting there) testimony of Professor Daniel Kobil, of 28 Feb 01.
So, the power is plenary. Should the President’s power be limited? Frankly, short of Amendment, I don’t think it can!