Here's how votes will be counted on Election Night and what to expect

CHICAGO - The director of the Fox News Decision Desk is warning of quirks in the way votes will be counted on Election Night.

Because of their vote counting procedures, some states will count Republican-leaning votes first. Others will open with Democratic-leaning vote totals.

What is important is who leads after everything has been counted.

In battleground Pennsylvania, a half-dozen Republican counties that voted for President Trump in 2016 now say they won't even begin to count mail-in-votes until Wednesday, as the president attacked a U.S. Supreme Court that ruled mail-in ballots are valid if they arrive by Friday.

“It allows cheating! It allows cheating on a very high level. And very easy cheating, too,” Trump said.

Although election officials said that is false and Republican lawyers provided no evidence of it in court, Trump added in a tweet that was flagged by Twitter: "[It] will undermine our entire systems of laws. It will also induce violence in the streets."

While Pennsylvania is a longtime part of the Democrats' "blue wall" that the president flipped in 2016, Joe Biden hopes to do the same to what might be called a Republican "red wall" in the south.

Three states that expect to report nearly all of their vote totals Tuesday night may tell the tale: North Carolina, Georgia and Florida.

President Trump needs to carry them all, as he did four years ago. Should Biden pick off even one, it would be a big boost to his chances of winning the White House.

One last word of caution: beware the "red mirage" and "blue mirage" as you watch the votes be counted Tuesday night. Because of quirks in state vote-counting systems like the one in Pennsylvania, it may appear that a state is going for one candidate when, in fact, by the time everything is counted, it will be a landslide for another candidate.