Americans have two days left to pick their new leader in a neck-and-neck presidential election likely decided by tens of thousands of votes in a handful of swing states.

Former President Donald Trump is hitting Pennsylvania, North Carolina and Georgia on Sunday, while Vice President Harris was focusing on Black voters and young voters in Michigan.

"In these next two days, we will be tested," Harris told the congregation at the Greater Emmanuel Institutional Church of God in Christ, in Detroit. "These days will demand everything we've got."

In his remarks Sunday, Trump suggested he "shouldn't have left" the White House after his election loss in 2020 and joked about the media being shot during the two assassination attempts against him.

Asked how her campaign would respond if Trump prematurely declares victory on Tuesday night — as he did in 2020 — Harris emphasized that U.S. elections and the U.S. voting system has integrity and can be trusted.

"I would ask, in particular, people who have not yet voted to not fall for his tactic, which I think includes suggesting to people that if they vote, their vote won't matter — suggesting to people that somehow the integrity of our voting system is not intact, so that they don't vote," Harris said.

"Everyone must know that their vote is their power to determine the outcome of the election, and their vote will count. It does matter," she told reporters.

Trump repeats his false claim that the election is being stolen

Trump started Sunday campaigning in Pennsylvania — a key swing state with 19 electoral votes, widely seen as a must-win for both the Trump and Harris campaigns.

During his speech at the Lancaster Airport, Trump told his supporters that this election is being stolen — a false claim he also made in the lead up to the 2020 election.

"We got a lot of crooked people out there — we're fighting like a son of a gun," Trump said while pointing to the press. "We're fighting. They are fighting so hard to steal this damn thing. Look at what's going on. Look at what's going on in your state every day. They're talking about extending hours and stuff."

The former president provided no supporting evidence of the election being stolen, but cast doubt on voting machines citing tech-billionaire Elon Musk, who is backing Trump and has used his ownership of X, the online platform previously known as Twitter, to push misinformation about the electoral process.

He also took swipes at a Saturday poll by J Ann Selzer, the widely respected Iowa pollster, that shows Trump 3 points behind Harris in Iowa — a state Trump easily won in 2016 and 2020.

"The polls are just as corrupt as some of the writers back there," Trump said. "They can make those polls sing. They brag about it. I got a poll — I'm 10 points up in Iowa. One of my enemies just put out a poll — I'm three down."

Trump also talked about what he called a failing U.S. economy and border, while also taking personal jabs at Harris calling her "low IQ."

"Kamala broke it, and we will fix it, and we're going to fix it fast," Trump said after arriving more than an hour late for his event. "America will be bigger, better, bolder, richer, safer and stronger than ever before."

Harris was focused on Michigan on Sunday. Tomorrow, it's Pennsylvania

Meanwhile, Harris was focused on the “Blue Wall" state of Michigan after campaigning in North Carolina and making a surprise appearance on Saturday Night Live in New York City. On Monday, she has a series of events in Pennsylvania.

For the fourth Sunday in a row, Harris attended a service at a Black church. She then worked the crowd at Kuzzo’s Chicken and Waffles in Detroit’s Livernois district, a restaurant owned by former Detroit Lions player Ron Bartell.

Harris also stopped by Elma's Barber Shop in Pontiac, Minch. where she spoke with local leaders and Black men. On Sunday night, she will have a rally in East Lansing, home of Michigan State University.

Black voters and college students are key to the coalition the Harris campaign needs to get her across the finish line in states like Michigan, where the race is tight.

Trump was scheduled to travel to Kinston, N.C., for another rally Sunday afternoon. He's then set to put on a third rally in Macon, Ga., — just 2 hours north of Kinston. The former president is scheduled to campaign in the Tar Heel state every day until the end of the election. Trump won North Carolina's electoral votes in 2016 and 2020, but polls show an increasingly tight race.

NPR’s Tamara Keith and Deepa Shivaram contributed to this story.