Trump cites 'secret tape' as supposed evidence Clinton 'wants to take in as many Syrians as possible'

Donald Trump accused Hillary Clinton of wanting "to take in as many Syrians as possible," referring to a "secret tape" as supposed proof that the Democratic presidential nominee would allow refugees to flood the US if elected.

"Wow, just came out on secret tape that Crooked Hillary wants to take in as many Syrians as possible," Trump tweeted. "We cannot let this happen - ISIS!"

The Republican presidential nominee has long argued that if the US continues to let in refugees fleeing the Syrian civil war, ISIS terrorists will find ways to slip into the country with them. Terrorists have been abusing the European system to slip in with the refugee flow and mount attacks on Western countries, but security measures in the US are generally thought to be more stringent.

Trump has repeated these claims about Clinton wanting to flood the US with refugees many times this election cycle. She has said that she thinks the US should be doing more to help the refugee crisis and has suggested admitting 65,000 refugees in fiscal year 2016. By comparison, Germany admitted more than 1 million refugees last year.

The video Trump was referencing in his tweet Monday is likely one from Project Veritas Action, a group run by controversial conservative activist James O'Keefe, who publishes undercover sting videos.

An undercover operative for the group attended an event with Huma Abedin, a top Clinton aide, and asked about Syrian refugees.

After thanking Abedin for addressing the Syrian refugee crisis and remarking that Islamaphobia is "rampant" in the US, the Project Veritas activist said, "You have to promise me, if Hillary is elected president, she's going to do everything she can to let these Syrians in."

Abedin responded, "Absolutely right."

The Project Veritas activist then said Republicans were trying to ban Syrian refugees from entering the US, to which Abedin responded, "Oh, and by the way, it's not just Republicans, there are some Democrats who are scared too."

She continued: "We need to have leadership on this, it is not, we can not turn these people away."

O'Keefe has previously gotten into hot water for his practices. In 2010, he pleaded guilty to a misdemeanor for posing as a phone repairman to enter then-Louisiana Sen. Mary Landrieu's New Orleans office. In 2013, he settled a suit for $100,000 after editing a recording with an ACORN employee who later lost his job.

Past O'Keefe footage has also been found to contain manipulative editing to show an intended narrative, as the conservative website TheBlaze wrote.

Allan Smith contributed to this report.