Democratic presidential candidate Kamala Harris and her Republican rival Donald Trump are targeting key swing states to win over undecided voters as they continue to crisscross the United States ahead of Tuesday's election.

The two contenders, who are in a tight race for the White House, will hold dueling rallies about 10 km (6 miles) apart on Friday evening in Milwaukee, the largest city in the battleground state of Wisconsin.

Milwaukee has the most Democratic votes in the state, but the conservative suburbs are home to the most Republicans and are a critical area for Trump as he tries to retake the state he narrowly won in 2016 and lost in 2020.

Four of the last six presidential elections in Wisconsin have been decided by less than one percentage point, or fewer than 23,000 votes, and this time the race is just as close.

After appearing at a campaign event in Las Vegas, Nevada on Thursday with music star Jennifer Lopez, Harris will welcome musicians such as GloRilla, the Isley Brothers and Flo Milli to Milwaukee. The campaign rally was also scheduled to feature Grammy-winning rapper Cardi B, who has more than 200 million followers across social media platforms.

Trump, meanwhile, will return to the Fiserv Forum, the venue where he officially accepted his party's presidential nomination at the Republican National Convention in July.

Before that, he is expected to make a campaign stop in Michigan, the Detroit suburb of Dearborn, home to a large Arab-American community.

Opinion polls, both nationally and in the seven closely divided states, show the two candidates nearly tied four days before Election Day. More than 66 million people have already cast their votes.

Trump has focused his campaign on stoking fears about violence he blames on immigrants and pessimism about the economy. The former president continues to falsely claim that his 2020 loss to President Joe Biden was the result of widespread fraud in multiple states, and he and his supporters have spread unfounded claims about that election in the key state of Pennsylvania.

On Thursday, Trump doubled down on his baseless claims that investigations into registration forms from suspected voters were evidence of voter fraud. Some of his supporters also claimed voter suppression as long lines formed to receive mail-in ballots this week.

“This sets the stage for attempts to overturn an election,” said Kyle Miller, a strategist at the advocacy group Protect Democracy. “We saw it in 2020, and I think the lesson Trump and his allies have learned since then is that they need to plant the seeds of these ideas early.”

State officials and democracy advocates said the incidents showed the system was working as intended. A judge extended the mail-in voting deadline in Bucks County, north of Philadelphia, by three days after the Trump campaign sued over claims that some voters were turned away before Tuesday's deadline.

Election officials discovered potentially fraudulent registrations in Lancaster and neighboring York counties, prompting investigations by local law enforcement. There is no evidence that the motions resulted in illegal votes.

“This is a sign that the built-in safeguards in our voter registration process are working,” Al Schmidt, Pennsylvania’s top elections official, told reporters this week.

Harris, meanwhile, warns against an authoritarian takeover, promises to help the middle class and opposes Republican abortion bans and restrictions.

One issue voters care most about is the economy. Many complain about inflation and wages not keeping up with rising prices.

Economists said the U.S. economy is actually in robust shape, fending off the remaining effects of the coronavirus pandemic with low unemployment and strong growth. However, new figures for Fridau showed drastically lower job growth last month, with just 12,000 new jobs created.

Analysts largely attributed this to knock-on effects from hurricanes and a strike at aerospace giant Boeing.