In a four-minute YouTube video, former Secretary of Labor Robert Reich warned of a “dirty Trump trick” voters need to look out for on Election Night.

“He used it in 2020 to try to overturn the election and he’s going to do it again,” Reich said. “But it doesn’t work if you know it’s coming.”

He said Trump will try to exploit what elections experts call the “red mirage” and prematurely try to declare victory before all the votes are counted.

Reich said that in almost every election, Republicans appear to take an early lead — the red mirage — which gets smaller throughout the night. He said this is the blue shift.

“This happens because Republican votes tend to be counted before Democratic votes,” Reich said. “It’s not magic. Votes are counted by precinct and Democrats tend to live in more densely populated urban precincts, while Republicans tend to live in more sparsely populated rural ones. It just takes longer to count the votes in a precinct with a lot of people than in a precinct with fewer people.”

As an example, he said there are more than 300 times as many people living in Fulton County, GA than in deep red Glascock County. Votes in the later country were obviously counted more quickly.

Reich also said that Democrats are more likely than Republicans to vote by mail and mail votes take longer to count.

“Anyone who follows elections knows about the red mirage and the blue shift, as the former political director of Fox News has testified” Reich said.

He then played a clip of former Fox News political editor Chris Stirewalt testifying before the Jan. 6 House Select Committee.

“In every election, certainly in a national election, you expect to see the Republican with a lead, but it’s not really a lead,” Stirewalt said in the clip, adding that it happens every time.

“But in 2020 Trump pretended the blue shift was surprising and suspicious,” Reich said, adding that it’s easy to see how people who don’t know about the red mirage could be tricked into thinking something unusual had happened.

“Trump’s nonsense claim that the votes counted earlier in the night were more legitimate than those counted later became the underpinning of the entire ‘big lie’, culminating on the Jan. 6 attack on the capitol,” Reich said.

He warned that the election will be close and that Trump will likely appear to be ahead early in the night and will again use that early lead to falsely claim victory.

“Mirages can be confusing, but if you know what they are, you won’t be fooled by them,” Reich said.