By the authority vested in me as President by the Constitution and the laws of the United States of America, including the Immigration and Nationality Act (INA) (8 U.S.C. 1101 et seq.), and in order to ensure the public safety of the American people in communities across the United States as well as to ensure that our Nation's immigration laws are faithfully executed, I hereby declare the policy of the executive branch to be, and order, as follows:

Section 1. Purpose. Interior enforcement of our Nation's immigration laws is critically important to the national security and public safety of the United States. Many aliens who illegally enter the United States and those who overstay or otherwise violate the terms of their visas present a significant threat to national security and public safety. This is particularly so for aliens who engage in criminal conduct in the United States.

 
Citation
David A. Martin, Trump’s Order on the Deportation of Undocumented Residents, Annotated by an Immigration Law Expert, Vox (January 31, 2017).