Ten years ago, the only reason anyone really talked about the need for the President of the United States to be a natural-born citizen was in connection with whether Arnold Schwarzenegger's mail would ever come to 1600 Pennsylvania Avenue. Today, it's a bit more heated than that; despite the presentation of fifty-year-old certificates and newspaper announcements, there are still quite a few people who believe that the evidence is a hoax and that Barack Obama (aka B-Rock "The Islamic Shock" Hussein Superallah Obama) was born outside the USA. Presumably, they also believe that a nice man in New York has a bridge to sell them and that once they hear back from that exiled Nigerian prince they'll be millionaires.
Although the meaning of "natural-born citizen" isn't defined within the Constitution, it has gained the established legal meaning of someone who was born an American as opposed to someone who acquired their American citizenship at a later date - this was an important consideration back in the eighteenth century, as it slammed the door on the possibility of European aristocrats coming over, starting a political storm, and ending up in the White House. Since then, the electorate has often had its hands full dealing with American aristocrats. Sure, it's practically unique when it comes to developed countries - not even as homogeneous a state as Japan has that kind of limitation written into its constitution (a constitution which, incidentally, was written by the United States).
For now, this is a sufficient definition... but I don't believe it'll stay that way forever. Why not? It's as simple as this - "natural-born citizen" doesn't necessarily have just the one meaning. Who defines what a "natural-born citizen" is in an age of genetic engineering?
Plenty of people have, shall we say, a thing against genetic engineering, most notably reflected in what seems to be a common reaction to genetically modified plants that end up in the human diet. The prevalence of the term "frankenfood" in the media tells you all you need to know about how a lot of people view it - that we're playing God, that we're going too far, nonwithstanding that humans have been genetically engineering plants for thousands of years by uprooting ones with attributes we don't like and planting ones with attributes we do like. The difference today is that genetic engineering is down to a science, and science is bad, mm'kay.
This opposition to genetically modified organisms manifests in a number of ways; recently, a group of anti-GM protestors in the United Kingdom threatened to destroy a test crop of wheat genetically tweaked for greater resistance against aphids, and over the weekend an organic farmer broke into the research centre and vandalized crops. Personally, outside the prospect of "terminator" genes - that is, food crops genetically modified for sterility, so that farmers have to continually purchase seeds from the manufacturer - I have difficulty understanding just what it is about genetically modified food that gets people so worked up.
Bear in mind that these are just genetically modified plants, and they're already getting this reaction. What the hell's going to happen when we have genetically modified *people*? Would a genetically engineered Presidential candidate face opposition because he or she wasn't "natural-born," but cooked up in some laboratory? The obvious answer, unless people really change their ways over the coming decades, is yes. When it comes to Obama and the birth certificate "controversy," what it comes down to is the claim that he's not American. When it comes to President Future, it would be as simple as suggesting that he or she isn't human.
Harsh? Yes... but wholly in line with what I've come to expect from people.