It’s the law

Adopted September 17, 1787

Article II — The Executive Branch

Section 1 — The President

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Before he enter on the Execution of his Office, he shall take the following Oath or Affirmation:

I do solemnly swear (or affirm) that I will faithfully execute the Office of President of the United States, and will to the best of my Ability, preserve, protect and defend the Constitution of the United States.

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Article IV — The States

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Section 4 — Republican government

The United States shall guarantee to every State in this Union a Republican Form of Government, and shall protect each of them against Invasion; and on Application of the Legislature, or of the Executive (when the Legislature cannot be convened) against domestic Violence.

It is not within the province of the courts to order the admission of foreigners who have no formal, legal connection to the United States. As to such persons, the decisions of executive or administrative officers, acting within powers expressly conferred by Congress, are due process of law.

Murray’s Lessee v. Hoboken Land and Improvement Co.; Hilton v. Merritt

It is an accepted maxim of international law that every sovereign nation has the power, as inherent in sovereignty and essential to self-preservation, to forbid the entrance of foreigners within its dominions or to admit them only in such cases and upon such conditions as it may see fit to prescribe.

Ekiu v. United States

The United States need only provide an aliens with a judicial trial when charging them with a crime and seeking a punitive sentence.

Wong Wing v. United States

Whatever the rule may be concerning deportation of persons who have gained entry into the United States, it is not within the province of any court, unless expressly authorized by law, to review the determination of the political branch of the Government to exclude a given alien.

Knauff v. Shaughnessy

Unadmitted, nonresident aliens have no right of entry to the United States as nonimmigrants, or otherwise.

Kleindienst v. Mandel

(Read more here.)

signed February 2, 1848 (Treaty with Mexico, binding on the United States and Mexico)

Article V

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The boundary line established by this article shall be religiously respected by each of the two republics, and no change shall ever be made therein, except by the express and free consent of both nations, lawfully given by the General Government of each, in conformity with its own constitution.

(See also the Gadsden Purchase.)

Section 8, Chapter 12, Subchapter II, Part IV, Section 1227.a.1.B

Any alien who is present in the United States in violation of this chapter or any other law of the United States, or whose nonimmigrant visa (or other documentation authorizing admission into the United States as a nonimmigrant) has been revoked under section 1201 (i) of this title, is deportable.

(See more from the USC here.)

Secure Fence Act of 2006

1. systematic surveillance of the international land and maritime borders of the United States through more effective use of personnel and technology, such as unmanned aerial vehicles, ground-based sensors, satellites, radar coverage, and cameras; and
2. physical infrastructure enhancements to prevent unlawful entry by aliens into the United States and facilitate access to the international land and maritime borders by United States Customs and Border Protection, such as additional checkpoints, all weather access roads, and vehicle barriers.

Illegal Immigration Reform and Immigration Responsibility Act (IIRAIRA) — 1996

The Illegal Immigration Reform and Immigrant Responsibility Act of 1996 (IIRAIRA) strengthened U.S. immigration laws, adding penalties for undocumented immigrants who commit crimes while in the United States or who stay in the U.S. for statutorily defined periods of time.

The Act was designed to improve border control by imposing criminal penalties for racketeering, alien smuggling and the use or creation of fraudulent immigration-related documents and increasing interior enforcement by agencies charged with monitoring visa applications and visa abusers. The Act also allows for the deportation of undocumented immigrants who commit a misdemeanor or a felony.

The Act mandates that immigrants who are unlawfully present in the U.S. for 180 days but under 365 days must remain outside the United States for three years unless pardoned. If they remain in the United States for 365 days or more, they must stay outside the United States for ten years unless they obtain a waiver. However, if they return to the U.S. without the pardon, they must wait 10 years until they may apply for a waiver.

(Read the full text here.)

Section 834b

(a) Every law enforcement agency in California shall fully cooperate with the United States Immigration and Naturalization Service regarding any person who is arrested if he or she is suspected of being present in the United States in violation of federal immigration laws.

(b) With respect to any such person who is arrested, and suspected of being present in the United States in violation of federal immigration laws, every law enforcement agency shall do the following:

(c) Any legislative, administrative, or other action by a city, county, or other legally authorized local governmental entity with jurisdictional boundaries, or by a law enforcement agency, to prevent or limit the cooperation required by subdivision (a) is expressly prohibited.