Men shown on camera standing behind Donald Trump during a rally were forced to make way for a line of smiling women, footage has showed.

In a campaign-style rally in Montana on Thursday evening, in which the US president railed against the media, Hillary Clinton, and the prospect of impeachment, young women were seen telling three men to make way so they could stand in their place.

One man who was visible over Mr Trump’s right shoulder was approached by a young woman in a black dress about 50 minutes into the president’s speech.

Woman in black dress tell man in green shirt to leave (Twitter/Fox News)

After speaking together for a few seconds, the man walked out of shot, while the woman stood smiling in his place.

Woman in black dress replaces man in green shirt (Twitter/Fox News)

The man, who failed to return, had earlier been caught on camera appearing to react in disbelief after Mr Trump claimed it was harder to win the electoral college than the popular vote.

“I beat Crooked Hillary, and the electoral college is hard, it’s frankly, if we didn’t know better, and maybe we’re starting to find out things we didn’t know, it’s hard, and harder to win than the popular vote,” Mr Trump said.

“Popular vote you go to three, four states and it’s boom boom boom – it’s like the 100-yard dash versus running the mile, you practice differently. She forgot that.”

Looking increasing perplexed, the man, who was not displaying any Trump memorabilia, appeared to repeatedly mouth “What?” as Mr Trump delivered his analogy.

After an hour, two men in 'Make America Great Again' hats, who were standing over Mr Trump’s left-hand shoulder, were apparently asked to leave by a young blonde woman in a blue dress.

Woman in blue dress tells two men over Donald Trump's left shoulder to leave (Twitter/Fox News)

They quickly moved out of view of the camera, replaced by the woman in the dress and another woman in a “President Trump” T-shirt.

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Woman in blue dress and woman in Trump T-shirt replace the two men (Twitter/Fox News)

Neither man returned for the remainder of the rally.

The bizarre switching around of Mr Trump’s almost exclusively white crowd came amid a speech in which the president once again raised the spectre of his own impeachment.

“You’ll have a country that’s going to turn into a third world country, because if the opposite country becomes president, every time before it even starts, before you’ve even found out whether or not he or she is going to do a great job, they’ll say we want to impeach him, and you’ll impeach him. It’s so ridiculous,” Mr Trump told the crowd in Billings.

“But, we’ll worry about that if it ever happens. But if it does happen it’s your fault because you didn’t go out to vote,” he said, to laughs from the audience.