As votes were being counted on election night, congressional candidate Jim Oberweis was ebullient.
Oberweis, a Republican from Sugar Grove, was leading Democratic U.S. Rep. Lauren Underwood for her 14th District seat. And if he won, he'd be moving from the state Senate to federal office – something he'd been unsuccessfully chasing since 2002.
Not only that, but President Donald Trump's reelection chances were looking good. Oberweis has been a vocal Trump supporter, and Trump had endorsed Oberweis.
"This could be a great, glorious night," Oberweis said.
But it was an illusion.
In the days that followed, Oberweis' lead evaporated. Underwood was in front by the weekend, and The Associated Press declared her the winner a few days later.
Underwood finished ahead by 5,377 votes, unofficial results showed – about 1% of the 400,908 total votes cast in the contest.
Oberweis, who intends to pursue a recount, wasn't the only suburban Republican who led on election night but fell behind as votes cast by mail were added to tallies.
So did Lake County State's Attorney Michael Nerheim, Lake County Board member Mike Rummel, Cook County Board of Review Commissioner Dan Patlak and DuPage County Auditor Bob Grogan.
Election watchers called the phenomena "the red mirage."
The COVID factor
More than 2 million Illinoisans voted using mail-in ballots in this election, according to the Illinois State Board of Elections. Nearly 2 million others voted early at in-person polling places.
The COVID-19 crisis was a factor in those totals. It led to systems being created in Illinois and other states that encouraged voting by mail over in-person voting because it was considered safer.
Illinois' legislation – good only for this month's election – also resulted in anyone who voted in 2018, 2019 or this year's primary automatically being sent applications for mail-in voting.
Savvy Democratic organizations then actively promoted voting by mail.
For example, Lake County's Democratic organization sent letters to registered voters detailing their options, including vote by mail, party Chair Lauren Beth Gash said. They also called people to inform them of those options and to motivate them to vote.
Meanwhile, Trump and other Republicans groused about possible election fraud in voting by mail. Relatively few promoted it.
"The Democrats had a messaging advantage," said Kent Redfield, professor emeritus of political science at the University of Illinois at Springfield.
'A Democratic lean'
Election results have shown most people who vote by mail back Democratic candidates.
"Vote by mail does have a Democratic lean," Redfield said. "New voters, particularly younger voters, find voting by mail very easy and low-cost in terms of time and effort."
On the flip side, Election Day tallies appear more Republican than the final totals.
For proof of this partisan split, look at the Underwood-Oberweis showdown.
In the Lake County portion of the 14th District, unofficial results showed Underwood received 13,323 votes by mail, more than double Oberweis' share of such votes.
Conversely, Oberweis got 8,464 Election Day votes in Lake County – nearly double Underwood's haul that day.
Likewise, in McHenry County, Oberweis received nearly twice as many votes on Election Day as Underwood but less than half the mail-in votes.
In the end, Underwood's total in the seven counties the 14th District reaches exceeded Oberweis'. According to her campaign, the 203,195 votes she received were more votes than any congressional candidate in the district's history – and voting by mail was a big factor.
"Our democracy is precious, and it requires participation," Underwood said in a news release. "I'm grateful to every voter for making their voice heard."
The Cook County Board of Review's Patlak was also on the other side of the red mirage.
The 1st District commissioner since 2010, Patlak, of Wheeling, lost to Democratic challenger Tammy Wendt of Palos Heights despite being ahead on election night.
As he watched vote totals update after the polls closed, Patlak saw they were lower than the numbers from his last election in 2016. And considering how anti-Trump sentiment was expected to drive more people than usual to vote, the total of counted votes as of election night likely was far lower than the number that actually had been cast.
The next day, Patlak learned some 300,000 mail-in ballots from suburban Cook County had yet to be counted – including tens of thousands from the 1st District.
As those mail-in votes were tabulated, Patlak's lead was whittled away. Wendt eventually pulled out front.
Patlak, who is concerned about possible inconsistencies in the vote totals and hasn't conceded, wasn't surprised by the vote-by-mail numbers or their Democratic slant.
"My mistake was that [I thought] they were being processed and would be counted on election night," he said.
What's the solution?
To prevent these situations from reoccurring, Redfield suggested state legislatures make two changes.
First, they should create long periods for voting by mail and early in-person voting. Second, they should change when such ballots are counted and reported to the public by county clerks and other election authorities.
Under state law in Illinois, officials can process and tabulate vote-by-mail and early ballots as they come in – staffers just aren't allowed to read or release the numbers before the polls close on election night.
Even so, not all process ballots that way.
In suburban Cook County, for example, all votes are counted at the same time on election night, precinct by precinct. But in Lake and McHenry counties, mail-in votes are counted after Election Day votes.
If states required election authorities to process – but not reveal – those votes as they come in, officials would be able to announce results from a much larger portion of the total ballots cast right after the polls close.
"This would eliminate [that] dramatic shift," Redfield said.
In close races like the one between Underwood and Oberweis, however, candidates may still move in and out of the lead because mailed ballots can arrive after Election Day.
In such cases, if voting by mail continues favoring Democratic candidates, red mirages might occur.
"There really is no fix for [that] situation," Redfield said.