Kamala Harris has said a second Trump term would be “a huge risk for America”, in a renewed effort to paint her Republican opponent as a threat to democracy, after the former president threatened to use US armed forces against those he has branded “the enemy within”.

At her own campaign rally in the battleground state of Pennsylvania, the US vice-president showed a montage of clips of Trump, including the former president saying “those people are more dangerous – the enemy from within – than Russia.”

At a speech in Coachella in California on Saturday, Trump referred to Democratic opponents as “the enemy within”, saying they posed a bigger threat to the US than the country’s foreign foes, and targeted Adam Schiff, a Democratic congressman who is running for the US Senate.

In an interview on Fox News the following day, he repeated the phrase to describe those he claimed were planning to create “chaos” on the day of the presidential election. He said the military should be deployed against them.

“A second Trump term would be a huge risk for America, and dangerous. Donald Trump is increasingly unstable and unhinged,” Harris told the crowd in Erie, Pennsylvania, after playing the clip.

She went on to say that Trump poses a danger because he believes those who do not agree with him are the enemy.

At the same time, Harris’s campaign released a new campaign advert, titled The Enemy Within, featuring some of Trump’s recent ominous comments about his adversaries and warnings from two former members of his presidential administration about the danger he would pose if elected.

The 30-second video, complete with footage of Trump walking in front of a row of helmeted riot officers and showing troops on the street during his presidency, tries to concentrate voters’ minds with contributions from Olivia Troye, a one-time national security adviser to Mike Pence, and Kevin Carroll, a former senior counsel in the Department of Homeland Security.

“I do remember the day that he suggested that we shoot people on the streets,” Troye says in the ad, which is accompanied with a dramatic musical soundtrack.

Carroll adds: “A second term will be worse. There will be no stopping his worst instincts. Unchecked power to no guardrails. If we elect Trump again, we’re in terrible danger.”

Harris, who has embarked on a late-campaign round of high-profile interviews after being accused for weeks of avoiding the media, is seeking to highlight the increasingly authoritarian tone Trump has been striking at his rallies.

Trump’s use of extreme language has coincided with an increase in his vitriol to describe Harris, who he last week described as “mentally impaired”. He called her “retarded” while addressing Republican fundraisers in September, the New York Times reported.

Harris’s campaign is also trying to draw attention to what it says a dearth of mainstream interviews given by Trump, who instead has chosen to make himself available to sympathetic interviewers, such as the rightwing radio host Hugh Hewitt.

“As of today, it has been **one month** since Trump’s been interviewed by a mainstream media outlet, as he has backed out of 60 Minutes and refuses to debate again,” Harris campaign spokesperson Ian Sams posted on Twitter/X.

By contrast, Harris is due to be interviewed on Wednesday by Bret Baier on Fox News, an outlet that is usually a go-to platform for Trump but unfriendly terrain for Democrats.