Two things are important to remember when talking about the United States Supreme Court.
1. The only way in which Obama could change the fundamental makeup of the Court is if a conservative Justice retires. Obama has appointed two Justices to the Court, none of whom will make a change for the worse in any future 2nd Amendment case. Why? Because the two Justices that retired, Souter and Stevens, both dissented in
Heller. Again in McDonald (decided after Obama's election and a USSC appointment), Stevens and Sotomayor dissented. There was no real change in the Court. Then next Justice likely to retire seems to be Ginsburg, who again will be replaced by someone will similar views on the 2nd Amendment.
If a Republican is elected, it is highly probable that Scalia and/or Kennedy will retire during that Republican's term, only to be replaced by another conservative (unless it's a Romney whitehouse
)
2. Supreme Court Justices don't act the way you think they will. If they did,
Roe v. Wade wouldn't be in force any more, and would have been overruled in
Planned Parenthood v. Casey, 505 U.S. 833 (1992). There, three "conservative" Justices appointed by Reagan and H.W. Bush (O'Connor, Kennedy, and Souter) all voted to affirm the fundamental holdings of
Roe.
Perhaps some of these "liberal" Justices appointed by Obama will surprise us.
Also, don't underestimate the power of stare decisis. Each year Heller and McDonald become more entrenched, and can be a very powerful factor in the Court's future decisions, no matter who the Justice is.