Segments of the right-wing blogosphere have become obsessed with the idea that Obama was born in Kenya, and was thus not a natural born citizen. Lawsuits have been filed with SCOTUS challenging Obama's status as a natural born citizen.
The basis of these claims is the Immigration and Nationality Act of 1952, which was in effect at the time Obama was born in 1961.
U.S. Citizenship Acquired by Birth Abroad
On December 24, 1952, the Immigration and Nationality Act of 1952 (the "1952 Statute") became effective. As under the previous statute, where both parents were U.S. citizens, one parent would have to have resided in the United States prior to the child's birth in order to transmit U.S. citizenship. The meaning of residence previously applied under the 1940 Statute was essentially the same as under the 1952 Statute.
In the case of a child born to one U.S. citizen parent and one alien parent, the U.S. citizen parent now had only to be physically present in the United States or its outlying possessions prior to the child's birth for 10 years, at least 5 of which were after the age of 14. "Physical presence" was different from the concept of "residence" which had applied under the previous statute. The physical presence requirement could be satisfied by mere presence in the United States even if the person had not established a legal residence there.
Since Obama's mother was three months shy of her nineteenth birthday when Obama was born, if Obama had been born in Kenya, he would not have been a U.S. citizen at birth under the law in effect at that time.
The law was amended in 1986 to relax the requirements for physical presence of the parent in the United States --
The Immigration and Nationality Amendments of November 14, 1986 further liberalized the transmitting U.S. citizen parent's physical presence requirements. For children born on or after November 14, 1986, a child born to one U.S. citizen parent and one alien parent would acquire U.S. citizenship if the U.S. citizen parent was physically present in the United States or its outlying possessions for at least 5 years, at least 2 of which were after attaining the age of 14 years.
As you can see, according to my source, the relaxed requirements were not retroactive. Either my source is mistaken, or there was subsequent legislation making the relaxed requirements retroactive.
NATIONALS AND CITIZENS OF THE UNITED STATES AT BIRTH
INA: ACT 301 - NATIONALS AND CITIZENS OF THE UNITED STATES AT BIRTH
Sec. 301. [8 U.S.C. 1401] The following shall be nationals and citizens of the United States at birth:
. . .
g) a person born outside the geographical limits of the United States and its outlying possessions of parents one of whom is an alien, and the other a citizen of the United States who, prior to the birth of such person, was physically present in the United States or its outlying possessions for a period or periods totaling not less than five years, at least two of which were after attaining the age of fourteen years: Provided, That any periods of honorable service in the Armed Forces of the United States, or periods of employment with the United States Government or with an international organization as that term is defined in section 1 of the International Organizations Immunities Act (59 Stat. 669; 22 U.S.C. 288) by such citizen parent, or any periods during which such citizen parent is physically present abroad as the dependent unmarried son or daughter and a member of the household of a person (A) honorably serving with the Armed Forces of the United States, or (B) employed by the United States Government or an international organization as defined in section 1 of the International Organizations Immunities Act, may be included in order to satisfy the physical-presence requirement of this paragraph. This proviso shall be applicable to persons born on or after December 24, 1952, to the same extent as if it had become effective in its present form on that date;