Over the weekend, Harris closed out a cross-country tour that included stops in battleground states Pennsylvania, Wisconsin, Michigan, Georgia and Arizona, as well as North Carolina and Nevada.

New polling released Saturday showed Harris taking the lead over Trump in Pennsylvania, Michigan and Wisconsin among likely voters. The New York Times/Siena College polls showed Harris at 50% among likely voters in each state, while Trump polled at 46%.

Vance, too, campaigned in key 2024 states and made the rounds on the Sunday shows. During his cable news appearances, Vance reiterated campaign talking points on immigration and repeatedly hit Harris for not sitting down for extensive media interviews and laying out her agenda. Harris has done brief gaggles with reporters and said she'd unveil an economic policy platform this week.

Sen. JD Vance told ABC News he blamed Vice President Kamala Harris and the Biden administration's policies, such as ending "Remain in Mexico," for the ongoing migrant crisis.

When asked how he and Trump would accomplish their stated goal of mass deporting as many as 20 million immigrants – a proposal experts previously told ABC News would be a "nightmare" -- Vance said they would take a "sequential approach."

"I mean do you go knock on doors and ask people for their papers? What do you do," Jonathan Karl, "This Week" co-anchor, asked.

"You start with what's achievable," Vance said. "I think that if you deport a lot of violent criminals and frankly if you make it harder to hire illegal labor, which undercuts the wages of American workers, I think you go a lot of the way to solving the illegal immigration problem."

"I think it's interesting that people focus on, well, how do you deport 18 million people? Let's start with 1 million. That's where Kamala Harris has failed. And then we can go from there," Vance said.

-ABC News' Ivan Pereira

Vice President Kamala Harris attended a fundraiser in San Francisco Sunday where she maintained her campaign "will win this election," but cautioned donors to "not take anything for granted."

"I know there's a lot of enthusiasm out there," Harris said, adding, "And you know, I've never been one to really believe in the polls -- whether they're up or they're down."

"What we know is the stakes are so high and we can take nothing for granted in this critical moment," she continued. "So we will fuel our campaign as we have, with enthusiasm and optimism, but also with a deep commitment to the hard work it’s going to take, and to campaign."

Speaker Emerita Nancy Pelosi introduced Harris at the event, touting the accomplishments of the Biden-Harris administration and the background of vice presidential nominee Tim Walz, several times calling the Harris-Walz ticket "the freedom ticket."

"[Harris] makes us all so proud. She brings us so much joy. She gives us so much hope," Pelosi said, calling the vice president "politically very astute."

-ABC News’ Fritz Farrow, Isabella Murray, Will McDuffie and Gabriella Abdul-Hakim

In his first sit-down interview since stepping down from the 2024 race, President Joe Biden explained his historic decision.

"Look, polls we had showed that it was a neck-and-neck race, would have been down to the wire. But what happened was a number of my Democratic colleagues in the House and Senate thought that I was going to hurt them in their races," Biden said earlier this week in an interview with CBS News that aired on Sunday.

He also pointed to the fact that he always saw himself as a transitional figure, and he said that beating Donald Trump was "the most important thing" for him.

"Number two, when I ran the first time, I thought of myself as being a transition president. I can't even say how old I am, it's hard for me to get out of my mouth. And, but things got moving so quickly, it didn't happen. And the combination was that I thought it was a critical issue for me still, it's not a joke, maintaining this democracy. But I thought it was important because although it's a great honor being president, I think I have an obligation to the country to do the most important thing, and that is we must, we must, we must defeat Trump," Biden said.

"It's a danger -- he is genuine danger to American security,” Biden said. “Look, we're at an inflection point in world history of the decisions we make in the last three, four years, the next three, four years determine what the next six decades look like, and democracy is the key."

-ABC News' Michelle Stoddart