Trump was introduced to the stage by Melania in an unannounced appearance.
The race for the White House remained essentially a dead heat on Sunday -- with nine days to go until Election Day.
Former President Donald Trump delivered a speech Sunday afternoon at New York's Madison Square Garden. After making several stops in Philadelphia on Sunday, Vice President Kamala Harris held a rally there Sunday afternoon.
Almost 42 million Americans have cast a vote through early voting methods, as of Sunday afternoon, according to data from the University of Florida's Election Lab.
The about 41.9 million recorded mail and early in-person votes were evenly split with about 21 million mail ballots returned nationally and about the same cast at in-person early voting polling sites across the country, the data showed.
Early voting options are now open to voters in 50 states and the District of Columbia. Many early voting periods will last until the weekend before Election Day.
Elon Musk took the stage at former President Donald Trump's campaign event at Madison Square Garden Sunday, leading the crowd in a "USA" chant and urging attendees to vote early.
Speaking at Madison Square Garden ahead of his running mate, vice presidential nominee Sen. JD Vance went to bat for former President Donald Trump while attacking the Democratic ticket.
"Now, on the eve of the most important election in our history, the greatest champion of them all, Donald J. Trump, has come to Madison Square Garden," Vance said.
"And I believe in just eight short days, we're going to turn the United States of America and make Donald J. Trump the president of the United States," Vance said.
Vance took aim at Vice President Kamala Harris for her previous comments, saying she wouldn't do anything different from President Joe Biden if elected president.
"She's running on how she's going to be different, but she couldn't name a single thing that she would do differently than Joe Biden. Now I will say that could be the Kamala Harris official campaign slogan, Kamala Harris, nothing comes to mind," Vance said, referencing Harris' recent appearance on "The View."
Earlier this month, Harris was asked whether there is anything she would have done differently than Biden over the past four years.
"There is not a thing that comes to mind in terms of -- and I’ve been a part of most of the decisions that have had impact,” Harris said.
-ABC News' Hannah Demissie
After comedian Tony Hinchcliffe disparaged Puerto Rico as "a floating island of garbage" at former President Donald Trump's Madison Square Garden rally on Sunday, Hinchcliffe is facing backlash from both sides of the political aisle.
Jenniffer González-Colón, a Republican who attended the Republican National Convention this year and is running to be the island's governor, called the comic's comments "despicable, inappropriate and disgusting."
Speaking with Minnesota Gov. Tim Walz in a Twitch stream Sunday, Rep. Alexandria Ocasio-Cortez called the remark "super upsetting."
"When you have some a-hole calling Puerto Rico 'floating garbage,' know that that's what they think about you. It's what they think about anyone who makes less money than them," Ocasio-Cortez said.
Earlier Sunday, rapper Bad Bunny shared Vice President Kamala Harris' video where she spoke about the island's future.
-ABC News' Joshua Hoyos
Vice President Kamala Harris delivered an unusually short stump speech at a campaign rally in Philadelphia on Sunday, leaving out some notable passages, including her riff about former President Donald Trump being "unfit" to serve.
"Philly, we've got nine days, nine days left in one of the most consequential elections of our lifetime. And we know this is going to be a tight race until the very end," Harris said to a crowd gathered at The Alan Horwitz "Sixth Man" Center. "So, we have a lot of work ahead of us, but we like hard work."
In her roughly 15-minute-long remarks, Harris mentioned Trump's name only three times, accusing him of being self-interested and for stoking "divisiveness" in politics.
"When you know what you stand for, you know what to fight for," Harris said. "And this election is about two extremely different visions for our nation: One, Donald Trump's, who has focused on the past and himself. And we are not going back."
During her remarks, Harris was briefly interrupted by protesters in the audience.
"I want to talk about Gaza for a minute. Okay?" Harris said, in the middle of her comments on Trump. "We can, and we must seize this opportunity to end this war and bring the hostages home. And I will do everything in my power to make that end."
-ABC News' Fritz Farrow, Will McDuffie and Gabriella Abdul-Hakim
