From the Document: "Immigration is a broad, multifaceted policy issue that involves temporarily or permanently admitting foreign nationals (aliens) into the United States and enforcing immigration laws. It is a perennial topic of congressional oversight and legislation. In recent years, the executive branch has taken the lead in implementing numerous policy initiatives, relying on discretionary authority conferred by statute. During the 115th Congress, the Trump Administration has pursued various immigration policies through executive branch action, including the imposition of entry restrictions known as the 'travel ban,' the termination of the Deferred Action for Childhood Arrivals (DACA) initiative, and the 'zero tolerance' policy regarding illegal border crossing. Courts have blocked some of these actions. For other proposals, such as constructing a border wall and restricting family-based immigration, the Administration has sought congressional action."
CRS In Focus, IF10520
Congressional Research Service: https://crsreports.congress.gov/