Donald Trump has reposted a crudely misogynistic comment about Kamala Harris on Truth Social in a move that reprised his past record of sexist behaviour and brazenly flouted pleas from members of his own party to emphasize issues over personal attacks.

With fresh polls showing Harris further improving her standing – and widening the gap with her opponent among women voters – Trump drew online opprobrium by sharing a vulgar post on his social media site implying that the Democratic nominee owed her political rise to sexual favours.

The post – originally posted by another user – featured photos of Harris and Hillary Clinton alongside the comment: “Funny how blowjobs impacted both their careers differently…”

The comment was an oblique reference to innuendo surrounding Harris’s former relationship with Willie Brown, the San Francisco mayor. The mention of Clinton – Trump’s defeated opponent in the 2016 presidential election – alluded to the affair between Monica Lewinsky, a former White House intern, and her husband Bill Clinton in the 1990s, which came close to ending his presidency.

It was not the first time Trump had made lewd references to Harris. On 18 August, he shared a video by the Dilley Meme Team, a group of rightwing content creators, to the soundtrack of a parody of the Alanis Morrisette song Ironic that contained the lines, “She spent her whole damn life down on her knees”, as an image of Brown appeared behind a picture of the US vice-president and her husband, Doug Emhoff.

But the latest post appeared among a flurry of other extreme posts on Wednesday that also included tributes to the QAnon conspiracy theory that holds that Trump is waging war against an elite network of Satan-worshipping pedophiles in government, business and the media.

He reposted: “WWG1WGA! RETRUTH IF YOU AGREE.” The acronym is short for the QAnon slogan: “where we go one, we go all.” He similarly reposted another QAnon phrase: “nothing can stop what is coming.”

The FBI has previously identified fringe theories like QAnon – which Trump has stopped short of endorsing while praising its supporters – as likely to fuel domestic terrorism.

In yet another incendiary communication, Trump posted manipulated images of some of his favourite targets – including the entrepreneur Bill Gates, Anthony Fauci, who spearheaded the US vaccine effort against Covid-19, Joe Biden and Nancy Pelosi – imprisoned and wearing orange jumpsuits.

The Harris campaign made no immediate response to Trump’s latest burst of social media activity, which followed disclosures of an altercation between his campaign team and staff at Arlington national cemetery, the resting place of fallen US military heroes, during a visit on Monday.

However, the CNN host Anderson Cooper – in a lengthy segment – said the posts took Trump’s previous campaigning to a “whole other level”.

“This is the Republican candidate for president and the 45th president of the United States, talking about two women who, no matter what you think of their politics, are two of the most accomplished women in American political history,” Cooper said.

Wednesday’s online outbursts came as a new Reuters/Ipsos poll showed Harris with a four-point nationwide lead, 45% to 41%, over Trump. Among women, the survey showed the vice-president increasing her lead to 13%, compared with an average of 9% in polls for July.

A separate Fox News survey showed Harris leading or increasing her support in four southern Sun belt states, all considered vital battlegrounds in November.

In a two-way race, Harris was up by one point in Arizona and by two points in Georgia and Nevada, while Trump is ahead by one point in North Carolina, according to the poll.

Beyond the polls, there was irritation among Republicans strategists who had previously urged Trump to desist from attacking Harris personally and focus on issues of concern to voters, such as the economy, inflation and immigration.

“I think people are incredibly frustrated,” Jason Roe, a former executive director of the Michigan Republican party, told the Washington Post.

He said Harris’s campaign and policy stances gave “opportunities for the Trump campaign to talk about issues that actually will matter to swing voters. And rather than doing that, he’s delving into this nonsense.”

Stuart Stevens, a member of the anti-Trump Republican group, the Lincoln Project, and a strategist for Mitt Romney’s failed 2012 presidential bid, challenged widespread predictions of a close election by suggesting that Trump’s approach would eventually alienate voters and enable Harris to win convincingly.

“There’s been a lot of talk – it’s sort of a universal truth – that this election is going to be close,” he told CNN. “I have a different opinion. I think it’ll be close till about October 20th, and then I think it’s going to be like Carter versus Reagan [in 1980, when Reagan won in a landslide], that the bottom is going to start to drop out [of Trump’s campaign].

“I think this is going to be a race that Democrats are going to win by more than Biden did,” he added.