Asked on Fox News last month whether he expected chaos on Election Day, Trump responded that the bigger problem was "the enemy from within."
"We have some sick people, radical left lunatics ... and it should be very easily handled by, if necessary, by National Guard, or if really necessary, by the military."
Trump, of course, will have no power to call out the military on Election Day, but his comments have alarmed critics, who say they suggest he views the armed forces as a potential weapon against opponents if he returns to the White House.
Trump repeated the term "the enemy from within" during an interview with popular podcaster Joe Rogan , saying they were more worrisome than Kim Jong Un, leader of nuclear-armed North Korea.
Trump has called for investigations into Harris, President Joe Biden, former President Barack Obama and Liz Cheney, a former US representative who is one of the most high-profile Republicans to turn against Trump.
At a September rally in Pennsylvania, Trump said Vice President Harris was responsible for the "biggest crime story of our time," referring to illegal border crossings. "She should be impeached and prosecuted for her actions," Trump said.
Trump has also shared posts on his Truth Social media platform calling for military tribunals to try Cheney and Obama.
On Oct. 25, Trump threatened an array of people with unprecedented levels of prosecution for potentially cheating on Tuesday.
"Please beware that this legal exposure extends to Lawyers, Political Operatives, Donors, Illegal Voters, & Corrupt Election Officials," Trump posted on Truth Social.
"Those involved in unscrupulous behavior will be sought out, caught, and prosecuted at levels, unfortunately, never seen before in our Country," he added.
Trump and his allies have been laying the groundwork to contest a potential loss in November by stoking doubts about the election's legitimacy. Trump has portrayed Democrats as cheaters, called mail-in ballots corrupt and urged supporters to vote in such large numbers to render the election "too big to rig."
Trump says he was the victim of widespread fraud in the 2020 presidential election, despite courts, state governments and members of his own former administration rejecting his claims.
Following pro-Palestinian protests on college campuses across the US this year, Trump told Fox News in July that anyone who desecrates the American flag should get a one-year jail sentence.
"Now, people will say: 'Oh it's unconstitutional.' Those are stupid people who say that," Trump said, adding that he wants to work with Congress to allow the jail sentences.
Trump has also said he would ban refugee resettlement from "terror-infested" areas such as Gaza and arrest "pro-Hamas thugs" who engage in vandalism, an apparent reference to the college student protesters.
Trump has also warned Meta CEO Mark Zuckerberg and Google over what he claims is potential election interference on their tech platforms.
Trump has accused Meta of suppressing content that would have hurt Biden in the 2020 election, and has also criticized Zuckerberg's donations to bolster election infrastructure.
"We are watching him closely, and if he does anything illegal this time he will spend the rest of his life in prison," Trump wrote his recently published Save America coffee table book, according to media reviews of the book.
Zuckerberg has not responded publicly to Trump's threat and has not endorsed a presidential candidate, but did say Trump's reaction to the July 13 assassination attempt was "one of the most badass things I've ever seen in my life."
Trump has also threatened to instruct the Department of Justice to criminally investigate Google for "only revealing and displaying bad stories about Donald J. Trump," according to a Truth Social post last month.
"I will request their prosecution, at the maximum levels, when I win the Election," Trump wrote. He provided no evidence for his assertion about Google.
Google has not responded to requests for comment about Trump's statement.
Trump and his allies have called for prosecuting, firing or jailing prosecutors who defy him or have investigated him.
In an April interview with Time, Trump said that if US Attorneys refused orders to prosecute someone, he would be open to firing them. "It would depend on the situation," Trump said.
Trump also said earlier this month that if elected he would fire Jack Smith, the federal prosecutor leading the criminal probes into his attempts to overturn his 2020 election defeat and alleged mishandling of classified documents after leaving office.
That follows an April 2023 speech by Trump - after Manhattan District Attorney Alvin Bragg convinced a New York grand jury to bring the first criminal charges ever against a former US president, in which he said Bragg was "the criminal."
"He should be prosecuted or at a minimum he should resign," Trump said. Trump's ally Steve Bannon, an influential voice in Trump's Make America Great Again movement, has said Bragg should be jailed.