US Vice President Kamala Harris lambasted Donald Trump on Friday for her White House rival's "violent rhetoric," saying his recent verbal attack on a Republican critic should disqualify him from becoming president again.
Trump has "suggested rifles should be trained on former representative Liz Cheney," Harris told reporters.
"This must be disqualifying. Anyone who wants to be president of the United States who uses that kind of violent rhetoric is clearly disqualified and unqualified to be president," she said.
Trump suggested Cheney should face combat with guns trained on her, comments his campaign said were intended to criticise her as a warmonger but which critics condemned as evidence he would target his enemies if he wins the presidential election.
"She's a radical war hawk. "Let's put her with a rifle standing there, with nine barrels shooting at her, okay?
"Let's see how she feels about it, you know, when the guns are trained on her face," Trump said at a campaign event in the battleground state of Arizona on Thursday.
Trump also criticised others in Washington who support US involvement in foreign conflicts.
"They're all war hawks when they're sitting in Washington in a nice building, saying, 'Oh, gee, well, let's send 10,000 troops right into the mouth of the enemy,'" he said.
Cheney, a former top Republican in the US House of Representatives, is one of the most prominent Republicans to turn against Trump during his third consecutive bid for the presidency.
She has endorsed Harris in Tuesday's election and has campaigned with her.
"This is how dictators destroy free nations," Cheney said on social media on Friday.
"They threaten those who speak against them with death. We cannot entrust our country and our freedom to a petty, vindictive, cruel, unstable man who wants to be a tyrant."
Arizona's top prosecutor says her office is investigating whether Trump violated state law for his comments.
Speaking to a local TV station, Arizona Attorney General Kris Mayes, a Democrat, said Trump might have violated state laws that prohibit death threats.
"I have already asked my criminal division chief to start looking at that statement, analysing it for whether it qualifies as a death threat under Arizona's laws," Mayes told 12News.
Mayes said it was not yet clear whether Trump's comment amounted to protected free speech or a criminal threat.
"That's the question, whether it did cross the line. It's deeply troubling," Mayes said. "It is the kind of thing that riles people up, and that makes our situation in Arizona and other states more dangerous."
The Trump campaign said his remarks had been misinterpreted.
"President Trump is 100 per cent correct that warmongers like Liz Cheney are very quick to start wars and send other Americans to fight them, rather than go into combat themselves," spokeswoman Karoline Leavitt said in a statement.
"This is the continuation of the latest fake media outrage days before the election in a blatant attempt to interfere on behalf of Kamala Harris."
Alyssa Farah Griffin, a top aide in Trump's White House, called his comments "unconscionable."
"I don't know how Republican leaders — many of whom served with Liz Cheney and at one point considered her a colleague and friend — cannot denounce this. It's dangerous. It's escalatory," she told CNN.
Trump has repeatedly talked about "the enemy from within" on the campaign trail and has vowed to prosecute political rivals, election workers, journalists and protesters, among others. He has said the military could be used against what he calls "radical left lunatics" if there is unrest on Election Day.
He also has vowed to pardon supporters who stormed the US Capitol on 6 January 2021, in an attempt to prevent Congress from certifying his defeat in the 2020 election.
While serving in Congress during Trump's 2017-2021 presidency, Cheney pressed him to keep US troops in Syria and restore harsh interrogation techniques for military detainees.
She lost her seat in Congress after helping to lead the investigation into the 6 January attack. Her father, Republican former Vice President Dick Cheney, has also refused to back Trump's third presidential run.
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