2024 election live updates: Crowd gathers for Trump's Madison Square Garden rally

President Joe Biden said former President Donald Trump poses a "genuine threat" to American democracy, during a visit to New Hampshire Democratic Party headquarters, saying, "We gotta lock him. Politically lock him up."

The remarks came after Biden listed Trump's proposals such as doing away with the Department of Education, taking on the federal civil service and the Supreme Court's recent decision granting presidents broad immunity. Biden said: "I mean, so I know this sounds bizarre. It sounds like - if I said this five years ago, you'd lock me up."

Then Biden said, referring to Trump, "We gotta lock him up. Politically lock him up. Lock him out, that's what we have to do."

"Lock her up" was an oft-repeated line by Trump and his supporters in 2016, a reference to Hillary Clinton's handling of classified information on her private email server.

Trump's campaign quickly seized on Biden's comments, calling on Vice President Kamala Harris to condemn the remarks and pushing claim that it shows Trump's legal battles are purely political -- charges prosecutors have repeatedly denied.

"Joe Biden just admitted the truth: he and Kamala's plan all along has been to politically persecute their opponent President Trump because they can't beat him fair and square," Karoline Leavitt, national press secretary of the Trump campaign, said in a statement. "The Harris-Biden Admin is the real threat to democracy. We call on Kamala Harris to condemn Joe Biden's disgraceful remark."

- ABC News' Justin Gomez, Lalee Ibssa, Soorin Kim, Kelsey Walsh

Former Democratic Rep. Tulsi Gabbard announced Tuesday she is officially joining the Republican Party.

Gabbard made the announcement during an appearance on stage at a rally for former President Donald Trump in Greensboro, North Carolina.

Gabbard has been stumping for Trump on the trail and recently advised him ahead of his Sept. 10 debate with Vice President Kamala Harris.

Her announcement Tuesday marks a further political shift after her run for the Democratic nomination for president in 2020.

"I'm proud to stand here with you today, President Trump, and announce that I'm joining the Republican Party," Gabbard said, calling the Republican Party the "party of equality" and "common sense" even as Trump repeatedly used insults to make personal attacks against his opponents during his own remarks.

"I am joining the party of the people ... and the party that is led by a president who has the courage and strength to fight for peace," Gabbard said.

"I'm looking forward to casting my vote for President Trump, because you are our best and only hope in this election to lead our country toward a future where every one of us can live in a truly free, peaceful and prosperous nation," Gabbard continued, stressing that "every single vote will count."

Eminem took the stage at a Harris rally in Detroit, Michigan, on Tuesday where he introduced former President Barack Obama.

"I'm here tonight for a couple of important reasons," Eminem said before sharing how much the city means to him. "Going into this election, the spotlight is on us more than ever," he said of the swing state.

The Grammy-winning artist encouraged the crowd to "get out and vote."

Eminem went on to endorse Vice President Kamala Harris, saying she supports a future where "freedoms will be protected and upheld" before introducing Obama to the stage.

The rally was held in Madison's Alliant Energy Center, which is able to hold more than 10,000 people. The event space was not completely filled -- only about two-thirds of the seats and floor space was taken.

Walz took aim at Trump and questioned his ally billionaire tech mogul Elon Musk, who Walz claimed was "the real running mate."

"So look, Elon's on that stage, jumping around, skipping like a dip*** on these things," Walz said to laughs.

"Seriously, where is Senator Vance, after he got asked the simplest question in the world at the debate, did Donald Trump lose the 2020 election? And after two weeks, he finally said, 'No, he didn't.' That's where he's been spending his time," Walz said.

Obama then came on stage and embraced Walz.

"Love that dude. Love that man. The kind of person who should be in politics," Obama said.

At three points during Obama's remarks at the Madison rally, which was billed as an event where the Democrats pushed early voting on the first day that in-person locations opened in Wisconsin, the former president utilized his old, famous saying: "Don't boo, vote!"

The crowd started to chant "Vote!" at the end of Obama's remarks.

"So whether this election is making you feel excited or scared or hopeful or frustrated or anything in between, do not sit back and hope for the best. Do not think this is a distraction or a joke. Get off your couch and do what? Vote," Obama said. "Put down your phones and do what? Vote. Vote for Kamala Harris as the next president of the United States. Vote for Tim Walz as the next vice president of the United States, vote for [incumbent Sen.] Tammy Baldwin and this whole incredible Wisconsin Democratic ticket."