WASHINGTON (Reuters) – Early vote returns in U.S. battleground states may not be a good indicator of whether Democratic nominee Kamala Harris or Republican rival Donald Trump will win, experts say, because of vote-counting rules and oddities from several key states.

In the 2020 election, some states showed a “red mirage,” with Trump leading on election night, before a “blue shift” saw Democrat Joe Biden overtake him as ballots were counted. vote by mail favored by more Democratic voters.

Pundits accurately predicted it would happen, but Trump still used the shift to amplify his bogus claims that the election was rigged.

It could happen again this week, especially in Pennsylvania, Michigan and Wisconsin.

The opposite — a “blue mirage” seemingly showing a strong result for Harris only for a “red shift” to reverse the trend — could also happen this week, particularly in North Carolina and Georgia.

Trump’s campaign team has said it plans to declare victory when his team believes he has surpassed the 270 Electoral College votes needed to win the election. This could be premature, depending on how many votes have yet to be counted and where they come from.

How it all plays out will depend on how and when the large number of mail-in or advance ballots in the various states are processed and counted.

Another factor is that Democrats tend to live in more populous urban areas, where vote counting takes longer.

There are seven battleground states that can decide the election, each with their own rules for handling and counting ballots. Here’s what to expect on Election Day and beyond:

PENNSYLVANIA

Pennsylvania did not have a clear winner in 2020 for four days after Election Day as officials sifted through a huge number of mail-in ballots.

The state is among the few that do not allow election workers to process or tabulate mail-in ballots until 7 a.m. ET on Election Day, meaning it will again be several days before the result is known.

With more Democrats than Republicans voting by mail, early results — based on in-person votes on Election Day — are likely to show Trump ahead, but his lead is likely to shrink as more mail-in ballots are counted .

This pattern in 2020 led Trump to falsely claim fraud. This year, a new law requires most counties to announce at midnight on election night how many mail-in ballots remain to be counted in an effort to prevent conspiracy theories.

WISCONSIN

Like Pennsylvania, Wisconsin does not allow election officials to process or count mail-in ballots until election morning, meaning there may be a delay in reporting the results of these early votes.

In addition, many of the state’s largest cities transport mail-in ballots to a centralized location for processing and tabulation. This may result in significant batches of votes being reported all at once early Wednesday morning.

In 2020, Trump and his allies falsely claimed fraud after Milwaukee, the state’s largest city, reported nearly 170,000 ballots around 3:30 am CT (0830 GMT), giving Biden a huge spike that moved him into the lead for the first time.

That increase was expected because of the way the city processes those ballots and the fact that Democrats were more likely to vote by mail. A similar model is likely in 2024.

GEORGIA

In-person early voting is popular in Georgia, where officials expected 65 percent to 70 percent of ballots to be cast at early voting locations.

Absentee or mail-in ballots, which can comprise about 5 percent of the vote, can be processed — which includes steps like verifying signatures — starting two weeks before the election, though workers must wait until Election Day to begin counting their.

All early votes — in person and by mail — must be counted and reported by 8:00 p.m. ET (0000 GMT) on election night, according to state law. Officials aim to have all votes, including those on Election Day, counted by midnight.

Ballots from overseas and military voters will be accepted up to three days after the election if postmarked by Nov. 5.

More than 21,000 such ballots have been requested, so the extremely close election may not be resolved until those votes are tabulated.

ARIZONA

Mail-in voting is extremely popular in Arizona; Nearly 90 percent of voters cast their ballots early, mostly by mail, in 2020. Arizona election officials can begin processing and tabulating mail-in ballots upon receipt, but results cannot be released until an hour after the polls close.

Any mail-in ballots on Election Day cannot be processed until the polls close. That’s often a sizable number — in 2022, those “late” votes accounted for a fifth of all ballots in Maricopa County, the state’s largest — and it can take days to count.

Early election night results should be mostly early votes, which could favor Harris, before the numbers shift to Trump as election day votes are counted. They could turn to Harris in the coming days as late-arriving mail-in ballots are tabulated.

MICHIGAN

Starting in the 2020 election, Michigan instituted in-person early voting for the first time and began allowing jurisdictions with more than 5,000 people to begin processing and tabulating mail-in ballots eight days before Election Day.

Smaller jurisdictions can do this the day before November 5th.

Officials hope these changes will allow the state to report results faster than in 2020, when mail-in ballots could not be processed in advance.

This created a “red mirage” on election night when early election day vote counts favored Trump. Biden ultimately surpassed Trump in terms of mail-in ballots, which took longer to count. Trump falsely claimed he was the victim of fraud.

NORTH CAROLINA

Election officials begin processing and scanning mail-in ballots before Election Day. After the polls close, the first results reported will likely be mostly mail-in ballots as well as early in-person votes.

Election Day votes will be counted and reported throughout the evening, with full results expected by midnight.

Harris may appear to lead early thanks to mail-in ballots, while Trump could close the gap as Election Day votes are counted.

If the election is as close as polls suggest, the outcome in North Carolina could remain unclear for a week or more. Absentee ballots arriving Nov. 5, as well as ballots from overseas and military voters, are counted during the 10-day period following Election Day.

In 2020, news outlets did not call North Carolina for Trump until November 13, 10 days after the election.

NEVADA

Nevada’s slow vote count in 2020 — news outlets didn’t call the state for Biden until five days after Election Day — has spawned countless memes, but officials say changes since then should speed up the process.

In particular, counties were allowed to begin processing and counting mail-in ballots on October 21.

In addition, workers can begin registering early votes in person at 8:00 a.m. PT (1500 GMT) on Election Day, rather than waiting until polls close.

But Nevada may not be called quickly. Mail-in voting has become popular in the state and is the only battleground that accepts late-arriving mail-in ballots.

Any ballot postmarked by Nov. 5 will still be counted if it arrives within four days. Historically, those late ballots favor Democrats, so there could be a swing to Harris as votes are counted after Election Day.

(Reporting by Washington Newsroom; Editing by Lincoln Feast.)