(CNN) It's a tried-and-true American tradition to stay up late on Election Night, watch results pouring in, and find out who the next President will be. But with a historic pivot toward mail-in voting due to the coronavirus, this Election Night could mark the beginning, not the end, of the process, and giving voters a false sense of who is winning, according to a wide array of experts.
Nonpartisan researchers call it the "blue shift." Democratic groups say it's a "red mirage." No matter the label, there's a very real phenomenon where Democratic candidates often gain votes as mail-in ballots get counted after Election Day. And this gap could be even wider this year.
CNN polls released last month found that a record number of voters plan to cast ballots in the mail, and that this surge is driven by supporters of former Vice President Joe Biden. Fueling this partisan divide is President Donald Trump's months-long public relations campaign against mail-in voting, which he has falsely said leads to widespread fraud and "rigged" elections.
It takes longer to count mail-in ballots, and in many states, ballots are still admissible if they are postmarked by Election Day but arrive later. In simple terms, this means the partial results that get reported on Election Night will probably look worse for Biden than the final, complete count.
This is exactly what happened in 2016: During Trump's victory speech, he was ahead in the national popular vote by about 950,000 votes -- and that is what viewers saw on television. But in the coming weeks, after all of the votes were tallied, Democratic candidate Hillary Clinton pulled ahead and won the popular vote, beating Trump by about 2.9 million votes nationwide.
The data firm Hawkfish, which was founded by former New York mayor and 2020 Democratic presidential candidate Michael Bloomberg, recently studied these scenarios and is warning the public about what they call the "red mirage." (Bloomberg now supports Biden, and Hawkfish is working for pro-Biden super PACs.)
According to their analysis, a Biden blowout could look like a comfortable Trump win on Election Night, based on partial results that come in quickly from in-person polling places that don't reflect millions of mail-in ballots that are still getting processed or haven't arrived. The analysis assumes that states that are new to this level of mail-in voting will suffer from similar delays.
"The way those results will look on Election Night, with those initial tallies, will be really different than the on-the-ground reality," Hawkfish CEO Josh Mendelsohn told CNN on Tuesday. "In so many places, those vote-by-mail ballots will have quite a lag. Let's be clear about what we're seeing on November 3rd, Election Night. Getting the narrative right is more important than ever."
Edward Foley, an election law expert who teaches at Ohio State University, has examined these post-election shifts. He warned in an August 2019 paper, published long before the coronavirus pandemic, that these fluctuations in the tally could trigger a national meltdown over the results.
According to Foley's research, the "blue shift" is very real in Pennsylvania. He found that the Democratic candidate picked up at least 22,000 votes after Election Day in the last four presidential elections. Typically, that isn't enough to sway the outcome -- but it could happen.
This also played out in the 2018 midterms, in a high-stakes Senate race in Arizona. Republican Martha McSally had a 15,403-vote lead on Election Night. But that turned into a 71,303-vote deficit as Democrat Kyrsten Sinema pulled ahead thanks to mail-in and provisional ballots.
With increasing alarm, Democratic groups are warning that Trump could seize on shifts like these to stoke chaos and reject the legitimacy of the results. Trump's campaign has said that he will respect the outcome of a fair election, though Trump has been less clear in his comments.
Mandi Merritt, a spokeswoman for the Republican National Committee, accused Democrats of exacerbating the situation by pushing states to accept more mail-in votes. This "absolutely leads to more questions, potential litigation, and larger shifts in the post-election vote count," she said.
Both presidential candidates and their respective parties are gearing up for a fight. Legions of lawyers are studying election laws in the battleground states and will be ready for litigation.
News networks, including CNN, are adapting their approach for Election Day, which many experts believe could turn into "election week." Some battleground states like Florida and Arizona have a strong track record of quickly counting mail-in ballots, so it's possible that news networks could project these pivotal states while waiting on slow results in other battlegrounds.
"The election results on Election Night are always partial, unofficial results," said David Becker, founder of the nonpartisan Center for Election Innovation and Research, which is working with states to inform voters about pandemic-era voting procedures. "We might be waiting longer and there might be more uncertainty, but the principles are the same that they have always been."