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.

"Of all the changes in personnel during this time of rapid change at the court, the Alito-for-O'Connor switch has clearly been the most consequential," said Paul Clement, who was top Supreme Court lawyer for then-President George W. Bush.

Indeed, nothing is likely to alter the court's current path in either direction unless President Barack Obama has the chance to replace a right-leaning justice, or a future Republican president gets to add another solid conservative vote.

The conservative trend on the court might be even stronger as long as Democrats hold Congress and the White House, said Paul Smith of the Jenner and Block law firm in Washington. "The conservative majority is going to continue to feel a need to push back in a lot of areas," Smith said.

The credit, or criticism, for many of the court's high-profile decisions goes variously to Chief Justice John Roberts, the putative leader of the court's conservatives, or Justice Anthony Kennedy, who dislikes the label "swing justice," but is always in the majority when the other eight justices split along liberal and conservative lines.

Their influence certainly was in evidence this term. Roberts was in the majority more than any other justice — 92 percent of the time — and Kennedy wrote the campaign finance decision as well as one in which the liberal justices prevailed, ruling out life prison terms with no prospect of parole for juvenile offenders in other than murder cases.