As experts and politicians debate the merits of President Donald Trump’s executive order limiting refugee flows from terror-prone nations, few have addressed the many warnings prior to Trump’s assumption of the presidency that Islamic State terrorist have long planned to infiltrate Western nations disguised as refugees.

Trump’s executive order, which many in the left have falsely described as a “Muslim ban,” temporarily halts the entry of individuals from seven nations listed in the Obama-era Terrorist Prevention Act of 2015: Syria, Sudan, Somalia, Libya, Iran, Iraq, and Yemen. The government is set to restore entry of refugees from these nations contingent upon establishing an orderly and competent screening process to prevent terrorists from posing as refugees and entering the United States.

In this sense, the executive order addresses a concern former CIA director John Brennan presented before the Senate Select Committee on Intelligence in June 2016, shortly after the massacre at Orlando’s Pulse nightclub orchestrated by an Islamic State sympathizer.

“ISIL has a large cadre of Western fighters who could potentially serve as operatives for attacks in the West,” Brennan said, using an alternate acronym for the Islamic State. “And the group is probably exploring a variety of means for infiltrating operatives into the West, including refugee flows, smuggling routes, and legitimate methods of travel.”

He noted that ISIS has also expanded its propaganda efforts to “inspire attacks by sympathizers who have no direct links to the group.”

These remarks came months after Brennan had warned against “hermetically seal[ing] our borders,” a statement he made at a forum in November 2015. Even before the Pulse massacre, Brennan nonetheless suggested U.S. officials should be “wary” of who enters the country.

Brennan was not the first to warn that Islamic State terrorists may pose as refugees to enter the United States. The same month Brennan suggested the U.S. should decline to “hermetically seal our borders,” Senator John McCain said in an interview he had reason to believe that Islamic State terrorists could pose as Syrian refugees to enter the United States. “I am sure that Baghdadi, the leader of ISIS, has already told some of these young men, go into the refugee flow and call us when you get to Berlin, New York, Paris, wherever it is,” he told New York radio host John Catsimatidis. “So we are going have to be very, very careful about what individuals we allow to come into this country as a result of this terrible tragedy.”

Senator McCain has since accused Trump of fueling “ISIS propaganda” by responding to the threat of Islamic State terrorists posing as Mideast refugees.

House Homeland Security Committee Chairman Rep. Michael McCaul also suggested in 2015 that intelligence he had been privy to suggested the Islamic State was seeking to infiltrate the West through refugee flows. “ISIS members in Syria have attempted to exploit [the refugee program] to get into the United States,” he told an audience at National Defense University. “The U.S. government has information to indicate that individuals tied to terrorist groups in Syria have already attempted to gain access to our country through the U.S. refugee program.”

The State Department has also indicated the U.S. is struggling with a concerted effort by Islamic State terrorists to enter the United States from Syria. “I wouldn’t debate the fact that there’s the potential for ISIS terrorists to try to insert themselves,” State Department Spokesperson Rear Admiral John Kirby said in September, adding that he believed those who have entered the United States have “all been extremely and very stridently vetted.”

The plan has succeeded in Europe. The Islamic State terrorist responsible for the New Year’s Eve massacre in Istanbul’s Reina nightclub, for example, entered Turkey through Syria with his wife and child, despite being an Uzbek national. Nearly a year before that attack, another Islamic State suicide bomber succeeded in killing 25 people in Istanbul, entering Turkey as a Syrian refugee. In Western Europe, four Islamic State terrorists cleared Syrian refugee vetting in October 2015, with two of them successfully attacking Paris.

At least one refugee with ties to the Islamic State has been arrested in the United States: Omar Faraj Saeed Al Hardan, an Iraqi refugee who pled guilty to “providing material support and swearing allegiance to ISIS” in a Texas court.