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Kamala Harris will attack Donald Trump as “unstable”, “obsessed with revenge” and “out for unchecked power” on Tuesday night, as she calls on Americans to reject her Republican rival and vote for her instead.

In one of the last big speeches of her presidential campaign, the Democratic vice-president will draw few punches as she criticises her opponent in this year’s White House race.

“Donald Trump intends to use the United States military against American citizens who simply disagree with him,” Harris will say, according to prepared remarks circulated by her campaign. “People he calls — quote — ‘the enemy from within’. This is not a candidate for president who is thinking about how to make your life better.”

“America, we know what Donald Trump has in mind: more chaos, more division and policies that help those at the very top and hurt everyone else,” she will add. “I offer a different path. And I ask for your vote.”

With just one week to go until election day, Harris will speak at Washington’s Ellipse, the site of Trump’s January 6 2021 speech in which he called on his supporters to “fight like hell” hours before they stormed the US Capitol in an attempt to halt Joe Biden from being declared president.

The vice-president’s campaign said the location had been chosen to draw a sharp contrast between her and her Republican opponent as she evokes the chaos of the riot at the Capitol.

“We are not at this location by accident. We believe the Ellipse is significant,” Jen O’Malley Dillon, Harris’s campaign chair, said on Tuesday. “It is a stark visualisation of probably the most infamous example of Donald Trump and how he has used his power for bad.”

The Harris campaign had initially estimated that some 20,000 people would attend Tuesday’s speech, but the National Park Service later confirmed the campaign had amended its permit application to accommodate more than 40,000 attendees.

The campaign has described Harris’s speech, which will take place with the White House in the background, as her “closing argument” with just a week to run in an increasingly tight race. The Financial Times poll tracker shows Harris and Trump in a virtual tie in the seven swing states that are likely to determine who wins the presidency.

“We know that there are still a lot of voters out there that are still trying to decide who to support or whether to vote at all,” O’Malley Dillon said. “We are very focused on making sure that we are doing everything in our power to reach the voters that are still making up their mind.”

Harris has shifted away from issues such as the economy in recent days and instead boosted her argument that Trump poses a grave threat to American democracy.

Last week, she attacked the former president for being “increasingly unhinged and unstable” after John Kelly, Trump’s one-time chief of staff, told The New York Times that Trump was an “authoritarian” who admired Adolf Hitler and fell into the “general definition of fascist”.

She has also criss-crossed the country with Liz Cheney, the conservative former Republican congresswoman who broke with Trump and her party over the 2021 Capitol attack and in September said she would be voting for Harris given the “danger that Donald Trump poses”.

The sober warnings stand in stark contrast to the image of a “joyful warrior” that the Harris campaign cultivated over the summer, after she replaced Biden at the top of the Democratic ticket.

But aides say her closing message will resonate with millions of voters who are frustrated by the coarseness and division that has plagued US politics in recent years.

Harris will pledge to seek “common ground” and be a president for “all Americans” and “always put country above party and above self”, according to the prepared remarks.

Trump’s own attempt at a closing argument at New York’s Madison Square Garden at the weekend was overshadowed by racist and misogynist comments, with one speaker describing Puerto Rico as a “floating island of garbage” and another comparing Harris to a prostitute with “pimp handlers”.

The Trump campaign — which has at times struggled to keep the former president focused on policy issues, such as the economy and immigration, where he has an edge with voters — on Monday hurried to limit the damage from the rally. But Trump showed little remorse on Tuesday, telling reporters at his Mar-a-Lago resort that the New York event was an “absolute lovefest”.