Two conservative-driven decisions with potentially broad consequences will likely define the just-completed Supreme Court term: freeing corporations and unions to spend as much as they like in campaigns for Congress and president, and ruling that Americans have a right to a gun for self-defense wherever they live.

A key member of the five-justice majorities in both cases, and the author of the guns opinion, was Justice Samuel Alito. Though he has been on the court less than five years, Alito has had an outsize influence in firming up the court's conservative bloc.

His appointment to replace the more moderate Sandra Day O'Connor, more than any other choice in the last decade shows the importance of Supreme Court nominations. It also points up that Elena Kagan's nomination to take the place of the like-minded John Paul Stevens almost certainly will not have the same short-term impact as Alito has had.