Look at the ages of the Supreme Court justices (N.B. I worked these out from birthdates, I may be a year out in some cases where they haven't had a birthday this year).

Pro Roe vs Wade:

J.P. Stevens - 88
R.B. Ginsburg - 75
D. Souter - 69
S. Breyer - 70
A. Kennedy - 72

Anti Roe vs Wade:

J. Roberts - 53
S. Alito - 58
A. Scalia - 72
C. Thomas - 60


All the pro-choice judges are over 69; all but one of the anti-abortion ones are 60 or under. And it only takes the balance to swing by one to tip the scales.

Unless we're very lucky, Roe vs Wade is likely to be overturned in a decade or too, and the supreme court is likely to aquire a more conservative tinge.

That said, the situation isn't quite as bad as it could be, because judges can choose when to retire, and hopefully liberal judges may choose to hang on for a few years if the president is a Republican, and, conversely, hopefully Stevens and maybe Ginsburg will choose to retire while Obama is still president, if he wins. But, still, the odds don't look good.