American Republicans, like Donald Trump and Jeb Bush, who warned against the Islamic State taking advantage of the refugee crisis, have been proven correct.

A senior German security official told the BBC Thursday that Islamic State "sleeper cells" have infiltrated the country, and that an attack would be "very likely."

"We have to accept that we have hit squads and sleeper cells in Germany," said Manfred Hauser, the deputy head of Bavaria's intelligence. "We have substantial reports that among the refugees are hit squads."

Some of those reports came from refugees, Hauser said, adding: "We have irrefutable evidence that there is an ISIS command structure that makes an attack in Germany very likely."

Last October, then-primary candidate Trump told Fox News' Bret Baier that if the U.S. accepted Syrian refugees without a thorough vetting process, "It could be the all-time great Trojan Horse." He said at the time that he was worried Islamic State operatives could be disguised among the refugees. In June 2016, Trump again warned that "a lot of those people are ISIS" when referring to Syrian refugees coming to the U.S.

Former GOP primary candidate Jeb Bush also expressed trepidation at the ability of the U.S. to properly vet refugees, suggesting America should prioritize "people like orphans and people who are clearly not going to be terrorists. Or Christians."

During testimony before U.S. senators, CIA Director John Brennan also warned the Islamic State would us "refugee streams, traditional smuggling routes and legitimate travel" to infiltrate the surrounding region. Brennan does not consider himself a Republican or a Democrat.

It calls into question those who cried "bigotry" at anyone who suggested the U.S. be cautious toward accepting refugees. Now we know some of the "refugees" really are members of the Islamic State, further proving those who called for caution over politics were right.

Ashe Schow is a commentary writer for the Washington Examiner.