Some states (see South Dakota) have passed laws banning virtually all abortions in defiance of Roe v. Wade on the basis that it is a state issue and not a federal issue.
You will notice that both Bush and McCain have said they will appoint “strict Constructionist judges” but they will not have an ideological “litmus test”.
A “strict Constructionist” judge is one who believes states should be able to decide on social matter such as abortion.
In other words, if a liberal member of the judge leaves under a President McCain, McCain can appoint a judge who isn’t necessarily “left leaning”, but who would push the issue back to the states if it ever came up.
And since states like South Dakota have passed these laws and others are trying to pass them, and of course organizations like Planned Parenthood are bringing lawsuits which are working their way up through the system to try to invalidate these laws, suit after suit after suit is filed up along the line until in a few years, when the court has at least 5 people who are either anti-abortion or pro states rights, hear the case, and decide that they need to overturn Roe v. Wade and make it a state’s issue.
Ergo, it doesn’t become illegal everywhere, but the more conservative states will ban the procedure.