Refugees, asylum seekers and immigrants are all heavily vetted, but refugees go through an especially strenuous vetting process. This extensive and thorough process is a coordinated effort between multiple U.S. government agencies under the Department of State and the Department of Homeland Security.
U.S. Citizenship and Immigration Services (USCIS), an agency under the Department of Homeland Security, facilitates the immigration process. By law, the agency is required to both protect the American public from threats to public safety and national security and fulfill its obligation under U.S. law to assist those fleeing persecution.
This fact sheet from USCIS provides information about security screening and background checks required by the U.S. Refugee Admissions Program (USRAP), and this infographic from the White House archives shows the many steps of multi-agency cooperation that occur during refugee resettlement.
The Department of State (DOS) is the managing agency that coordinates with several other government and non-government partners to facilitate the USRAP. USCIS is responsible for the interviewing and application processing for all refugees that enter the U.S. and currently conducts all interviews in person. They are supported in this process with information and assistance from multiple federal intelligence, counterterrorism, and law enforcement agencies.
While the screening process is not the same for all immigration avenues, it’s worth noting that studies show that immigrants are less likely to commit crimes than native-born US Citizens. There is no logical basis or evidence to say that immigrants create a security risk.