The law has been changed and defined about every 20 years or so.
The last time being in 2005 under the Bush Admin and a Republican controlled congress.

§ 1401. Nationals and citizens of United States at birth

Title 8 of the US Code as currently published by the US Government reflects the laws passed by Congress as of Jan. 5, 2009



TITLE 8 > CHAPTER 12 > SUBCHAPTER III > Part I > § 1401Prev | Next § 1401. Nationals and citizens of United States at birth

The following shall be nationals and citizens of the United States at birth:
(a) a person born in the United States, and subject to the jurisdiction thereof;
(b) a person born in the United States to a member of an Indian, Eskimo, Aleutian, or other aboriginal tribe: Provided, That the granting of citizenship under this subsection shall not in any manner impair or otherwise affect the right of such person to tribal or other property;
(c) a person born outside of the United States and its outlying possessions of parents both of whom are citizens of the United States and one of whom has had a residence in the United States or one of its outlying possessions, prior to the birth of such person;
(d) a person born outside of the United States and its outlying possessions of parents one of whom is a citizen of the United States who has been physically present in the United States or one of its outlying possessions for a continuous period of one year prior to the birth of such person, and the other of whom is a national, but not a citizen of the United States;
(e) a person born in an outlying possession of the United States of parents one of whom is a citizen of the United States who has been physically present in the United States or one of its outlying possessions for a continuous period of one year at any time prior to the birth of such person;
(f) a person of unknown parentage found in the United States while under the age of five years, until shown, prior to his attaining the age of twenty-one years, not to have been born in the United States;
(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 288 of title 22 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 288 of title 22, 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; and
(h) a person born before noon (Eastern Standard Time) May 24, 1934, outside the limits and jurisdiction of the United States of an alien father and a mother who is a citizen of the United States who, prior to the birth of such person, had resided in the United States.

http://www.law.cornell.edu/uscode/8/1401.html

Ok. So if the " anchor baby " is a myth....

Then why is it being taken as the " norm "???

It is real. Pregnant women with micas, get medical care here, have their kids here. It's all legal. There are even some who jump the border to have their kids here.

It's easy for someone who doesn't see it, to believe it.