It has been a long tradition for US television networks to call projected winners on election night as results trickle in -- but the unique circumstances of 2020 are likely to create numerous challenges to that practice.
"Decision desks" set up by media outlets to project winners of each state, which will determine the presidential race, are gearing up for a complicated election night amid uncertain timing for counting of mail-in and absentee ballots and fears about premature claims of victory.
In a campaign marked by the Covid-19 pandemic, the old methods of exit polls are less useful than in the past, says Costas Panagopoulos, chair of political science at Northeastern University and a member of the NBC News decision desk team.
"With the rise in early voting, absentee and mail-in voting, it's no longer the case that we can survey voters at the polling places and make accurate predictions," Panagopoulos said.
Some fear an early tally based on votes cast in person on election day may distort the outcome and prompt President Donald Trump to claim victory before absentee and mailed ballots are counted, opening up the potential for chaos.
"It's entirely possible there will be discrepancies across networks because each network has its own standards for how they reach projection decisions even though they are all using virtually the same data," Panagopoulos said.
CBS News said its decision desk will combine exit poll data and vote tallies with the network's proprietary polling and surveys of some 100,000 people around the United States.
Some analysts have warned of a "red mirage" which would show Trump ahead based on early vote counts, even if the absentee ballots counted later reverse the trend -- a result which could prompt an outcry.
"The contest will be won not only at the ballot box and in the courts but in the court of public opinion," said a Guardian essay by more than 20 members of the American Political Scientists Association.
"All media should adopt the strict standard that no state winner should be declared until the number of votes remaining to be counted has been certified to be less than the margin between the two major-party candidates."
A newly formed National Task Force on Election Crises has called on media organizations and the National Election Pool which gathers data for the outlets to use extra caution for projections on November 3.
"This presidential election will be like no other in our history," said a letter from the task force which includes academics, former elected officials and activists, to media organizations.
The coalition said that as many as 70 percent of all ballots cast may be by mail or other absentee methods, and that the tallying will depend on different rules for each of the 50 states.
"It could take days or weeks to complete an accurate count of all votes," the letter said.
"This period of uncertainty will add further pressure to an already strained system and allow bad actors to attempt to undermine our democratic process."
The different processing times in various states could lead to uncertainty, according to Joe Lenski, chief executive of Edison Research, which provides exit polls and vote count data to the National Election Pool.
"Some states don't even allow the by mail ballots to be opened until election day, Lenski said.
"So we're expecting those states based upon what we saw on the primaries to take a lot longer processing and report their by mail ballots. In some cases it could be days or weeks."
While a handful of media outlets will be making calls, one being closely watched is Fox News, a favorite of Trump and Republicans.
Fox said in a statement that it will be collecting data and making projections without bias.
"The integrity of our decision desk is rock solid," a Fox statement said.
"We will call this presidential election carefully and accurately, relying on data and numbers."
Fox decision desk chief Arnon Mishkin told a recent podcast on the network that making calls will be complicated by the new voting patterns but touted a new tool "that is actually optimal for measuring how people are voting in an election where over 60 percent of the people are not going to be exiting poll on election day."
Despite the fears, a Pew Research Center survey found 82 percent of US adults have confidence their main news sources will make the right call, with slightly more confidence among Democrat Joe Biden's supporters.