"In light of the terrorism in San Bernardino ... it appears that DHS’s policy of willful blindness toward the reality and danger of radical Islam in the United States contributed to the death of 14 Americans here at home," he said in a letter to top Department of Homeland Security officials, including Secretary Jeh Johnson.
The Texas senator, who is running for president, sent a letter Friday to Johnson, Deputy Secretary Alejandro Mayorkas and Leon Rodriguez, the director of U.S. Citizenship and Immigration Services, calling the social media policy "exceedingly dangerous" and "nothing short of colossal negligence."
Lawmakers have pressed the administration to include social media in background checks after one of the shooters in the California incident was said to have posted a message on Facebook declaring allegiance to the Islamic State in Iraq and Syria (ISIS) before the attack.
While FBI Director James Comey said last month that the messages discussing extremism only occurred on private message, DHS officials have defended their practices, saying that they do include social media occasionally in the background check process for visa applicants.
Cruz, however, suggested the DHS's social media rule was part of a broader trend from the administration on policies that "restrict fraud and terrorism investigators from fulfilling their missions and (arguably) enable fraudulent and dangerous people to enter and remain in the United States."
The Texas Republican is asking the department to preserve all internal documents or information on using social media for investigations. He added that destroying any requested documents could be a criminal offense and that he hopes the next president will "pursue justified prosecutions with all due energy."
Cruz also wants to know if the DHS believes it is currently against the law for its officials to screen social media as part of the visa background check process, or if they consider social media postings private communications.
He also wants details on any steps Homeland Security has taken to implement a new social media policy, including pilot programs, or if there is a current policy that allows officials to look at publicly available social media content.