A right-wing US commentator who may have been the source of the videos tweeted by Donald Trump has admitted she did not know who Britain First were and did not attempt to check them out before spreading their messages online.
But Ann Coulter said there was no need for her to check the the far-right group's messages, telling BBC Radio 4's Today programme: "A video is a video is a video."
Ms Coulter said Mr Trump was within his rights to criticise the Prime Minister of a close ally online, saying: "Yeah, after she attacked him? Sure."
She said: "I think he has only given as good as he gets. I think he has been verbally attacked from the mother country for a lot longer than he has been attacking Britain."
Ms Coulter is one of just 45 people Mr Trump follows on Twitter, and it is thought he may have retweeted three videos posted by Britain First after seeing them on her timeline.
Asked if she knew who Britain First - described by British Communities Secretary Sajid Javid as "a vile, hate-filled racist organisation" - were before sharing their clips, she said: "No... I don't think it really matters, it's a video."
So POTUS has endorsed the views of a vile, hate-filled racist organisation that hates me and people like me. He is wrong and I refuse to let it go and say nothing— Sajid Javid (@sajidjavid) November 29, 2017
Ms Coulter confirmed she had not even checked the Twitter biography of Britain First leader Jayda Fransen, who originally sent out the message.
"I have a little tip for you," she told interviewer Nick Robinson. "You need to spend a little time on Twitter and figure out that people retweeting videos are not researching the bios of the people who sent the video. A video is a video is a video. It's not a fake video."
Confronted with the suggestion that she was spreading "fake news" by claiming one of the films showed a "migrant" beating up a Dutch man, when in fact both people pictured were citizens of the Netherlands, Ms Coulter said: "Nobody cares about `migrant' against 'child of migrant'. He is not a 10th-generation Dutchman, he is beating up a 10th-generation Dutchman."
She added: "Anybody can look at this video and see it is a Middle Easterner. If you would prefer, we'll say 'Middle Easterners born in the Netherlands', but if you don't accept that, we're going straight back to `Middle Eastern' in another 30 seconds. It could not be more supremely irrelevant - it is a difference without a distinction.
"The issue is all these Middle Easterners and Muslims being brought in. To pretend there's no difference between a 10th-generation Dutch person and a migrant or the child of a migrant is preposterous.
"This is what Brexit was about, this is what Donald Trump is about. The native countries are blowing up at the constant importation of people who do not share our Western values. That's the point at issue."
Asked whether she would treat all Christians as a threat on the basis of mass shootings in the US perpetrated by people of Christian background, Ms Coulter said such massacres were "quite rare per capita".
She added: "What I want, as did Donald Trump in his first policy paper when he was running for president, is a moratorium on all immigration for a while. You guys have the Muslims, we have the Central Americans and the Muslims. It's just too much. We can't assimilate them. They are breaking the welfare system. It is hurting the poorest Americans."