Can the President Close the Border? Relevant Laws and Considerations [April 12, 2019] [open pdf - 587KB]
From the Document: "This Legal Sidebar identifies the statutes and legal issues most relevant to the President's statements about closing the border. The analysis is necessarily general. The Trump Administration has not released a plan with details about specific measures or underlying justifications. An executive decision to close some ports of entry to certain categories of non-U.S. citizens would require a different legal analysis than would a decision to completely seal the ports on the southern border to all goods and persons seeking to enter the United States, including U.S. citizens and lawful permanent residents (LPRs). Moreover, the relationship between any border closure measures and the justification that the Executive articulates for them would bear on the legal analysis. In the absence of a concrete proposal, the discussion here mainly sets out the primary relevant authorities and the considerations that they trigger."
CRS Legal Sidebar, LSB10283
Congressional Research Service: https://crsreports.congress.gov/