The US is a country of immigrants, and without this law a foreign element may get control of it. It does make sense, it seems to me. Could a US born person still bear more loyalty for another country than the US? Clearly so, and yet it would be easier for another country to insert its own charismatic figure and fund them heavily, in order to get power of the US, than to find a US born one. With a US born person you have a better idea of their history and can try better to decide whether they are a foreign agent than non-US born one.
People who are not born in the US often find it very hard (or impossible?) to even get security clearance to work, for example, for the NSA (National security agency). Let alone such a high security clearance as the president needs to get.
I believe the incidence of home grown terrorists (jihadists) is on the rise - sort of knocks the notion that home-grown equals loyalty on the head. And I would imagine that anyone elected to the presidency in the US has de facto maximum security clearance, unless the CIA and what-have-you are running a parallel and covert government. I suppose that is not beyond the realm of possibility. Probably make a good book, that possibility would.
