2024 election live updates: Bruce Springsteen performs at Harris rally

During a call into the "Hugh Hewitt Show," Trump said one of the first things he'd address if reelected would be to terminate special counsel Jack Smith.

"It's so easy. I would fire him within two seconds," Trump said during the call.

"I don't think they'll impeach me if I fire Jack Smith. Jack Smith is a scoundrel. He's a very dishonest man, in my opinion, very dishonest man," he continued, adding that he was going to sue Smith.

Harris's campaign was quick to criticize Trump for his comments.

"Donald Trump thinks he's above the law, and these latest comments are right in line with the warnings made by Trump's former Chief of Staff that he wants to rule as a dictator with unchecked power," Harris campaign spokesperson Ammar Moussa said in a statement.

"A second Trump term, where a more unstable and unhinged Trump has essentially no guardrails and is surrounded by loyalists who will enable his worst instincts, is guaranteed to be more dangerous. America can't risk a second Trump term," Moussa added.

Fred Upton, a former GOP congressman who voted to impeach Trump over the Jan. 6 attack on the U.S. Capitol, is endorsing Harris for president.

He joins a growing list of other Republicans, including Adam Kinzinger and Liz Cheney, in backing the Democratic nominee over concerns about Trump's role in the unrest.

"Today, I'm joining more than 30 former Republican members of Congress who publicly refused to support Donald Trump, and I'm proud to say that I've already cast my ballot for Kamala Harris," Upton told reporters on Thursday.

He added, "I've never before voted for a Democrat for president, and I honestly never thought I would, but she's strong, committed public servant. She's running to put people together, strengthen our economy and protect our fundamental freedoms."

Upton, who served 30 years in the House, said impassioned fights about policy were always the norm but "with Trump in charge, politics was more personal, more angry and more divided than ever before."

Superstar Beyoncé is set to appear in her hometown with Harris during the vice president's planned rally in Houston, Texas, on Friday, according to two sources with Harris' presidential campaign and the White House.

The musician was thought to be on the program for the Democratic National Convention in Chicago, but she did not end up performing despite headlines saying she was planning to. The buzz around the potential performance was notable.

Friday's event is slated to be focused on reproductive health care. Beyoncé has spoken publicly about her own fertility journey.

The moment comes as Democrats are hopeful that their Texas Senate candidate Colin Allred is surging, though he remains behind in the polls.

-ABC News' MaryAlice Parks, Gabrielle Abdul-Hakim and Molly Nagle

With just 12 days left in the campaign, Harris on Thursday will do local media interviews in Georgia before a 8 p.m. ET rally with former President Barack Obama and concert with Bruce Springsteen.

Trump will be in Arizona for a rally at 5 p.m. ET before going to Nevada for a Las Vegas rally hosted by Turning Point Action at 10 p.m. ET.