Veteran U.S. Senator John McCain has raised the specter — again — of terrorists entering the United States from Canada.

On Wednesday evening, during an interview with CNN, McCain expressed concern about ISIS extremists entering his country through either the south or north.

"Today we had a hearing and there was testimony from counter-terroism people and the Department of Homeland Security. There is Twitter traffic right now and Facebook traffic where they are urging attacks on the United States of America," the Republican senator said, as part of his response to a President Barack Obama address to the nation.

"And there is a great concern that our southern border and our northern border is porous and that they will be coming across."

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This isn’t the first time that McCain has taken a shot across the border, if you will,

According to the National Post, in 2009, McCain backed-up then-Homeland Security Secretary Janet Napolitano’s assertion suggesting that some 9/11 terrorists came to the United States via Canada.

"Well, some of the 9/11 hijackers did come through Canada, as you know," McCain told Fox News, at the time.

That comment, however resulted in a strong rebuke by both the Canadian embassy and then-finance minister Jim Flaherty.

"It is unfortunate that what is a statement that is not true is repeated from time to time. It’s just factually wrong," Flaherty said, according to the Post.

"The secretary [Ms. Napolitano] the other day made clear she was mistaken when she said the same thing. So I would hope people wouldn’t want to make statements that are inaccurate so we don’t hear much of that anymore."

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Despite those rebukes, that belief — that terrorists can somehow find their way through Canada to the U.S. — seems to be alive and well.

And it’s not only McCain.

Earlier this week, investigative journalist and filmmaker James O’Keefe posted a video of a fictitious ISIS terrorist with Ebola taking a boat across Lake Erie from Ontario to Cleveland, Ohio.

According to O’Keefe, the actor didn’t get caught.

"The British government says American journalist James Foley’s ISIS assassin was an Englishman,’ O’Keefe says in the video.

"British intelligence believes more than 500 British citizens have joined ISIS. Brits can enter Canada without a visa; it’s virtually an open door."

Here’s the video:

For their part, the Harper government didn’t comment directly on McCain’s comments.

They did however want to boast about their record on strengthening the border and combating terrorism since 9/11.

"I cannot comment on operational matters of national security, I can say that the Strengthening Canadian Citizenship Act, received Royal Assent. It will strip the Canadian citizenship from dual-nationals who engage in acts of terrorism or fight against the Canadian Armed Forces abroad," Jason Tamming, a spokesperson for Public Safety Minister Steven Blaney, told Yahoo Canada News in an email exchange.

"In addition, we passed the Combating Terrorism Act and introduced Canada’s first counterterrorism strategy - a four pronged approach to prevent, detect, deny resources and respond to terrorist activity and threats.

"Since forming Government in 2006, we have increased the number of front line border guards by 26 per cent."

(Photo courtesy of Reuters)

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