Joe Biden has framed a nail-bitingly close race for governor of Virginia as a referendum on his young presidency and an opportunity to rebuke his predecessor, Donald Trump.

Seemingly liberated from the formal trappings of office by a return to the campaign trail, Biden used a rally in Arlington, Virginia, to launch an unusually scathing and sustained attack on the former president.

Biden had made the short journey from Washington to speak in support of the Democrat Terry McAuliffe, who faces a tight election against the Republican Glenn Youngkin next week.

“Just remember this: I ran against Donald Trump,” he told an estimated 2,500 people gathered in a park on a chilly Tuesday night. “And Terry is running against an acolyte of Donald Trump.”

The election in Virginia is seen as the most important of the year, offering a window on to public sentiment about Biden’s first nine months in office and a preview of what to expect in next year’s midterm elections for Congress.

McAuliffe, a former governor seeking to return to the post, is a career politician and establishment Democrat long associated with Bill and Hillary Clinton. Youngkin, by contrast, is a business executive who has never held elected office.

Polls once gave McAuliffe a clear lead in a state where no Republican has won statewide office since 2009, and where Biden beat Trump by 10 percentage points last year. But Youngkin has been closing the gap, hammering away at “culture war” issues in schools as part of a bid to peel off suburban votes.

Biden, speaking at a McAuliffe rally for the second time, was greeted by enthusiastic cheers but also heckled by climate activists during his remarks. He said: “It’s not a Trump rally. We let ’em holler.”

He went on to confirm that the state-level race has taken on a national significance. Biden ran through McAuliffe’s accomplishments as governor, for example on gun safety, and his own presidential record on issues such as the coronavirus pandemic.

He also noted how Youngkin has been walking a fine line between accepting Trump’s endorsement and barely mentioning him in speeches, a sign that the former president is toxic to most Virginians.

Youngkin had begun his campaign calling for “election integrity” to ally himself with Trump’s “big lie”, the false claim that the 2020 election was stolen, Biden said. “It was price he had to pay for the nomination and he paid it. But now he doesn’t want to talk about Trump any more. Well, I do.”

The president elicited laughter from the crowd by saying: “Talk about an oxymoron: Donald Trump and election integrity?! I can’t believe he put the words Trump and integrity in the same sentence.”

Biden lambasted Trump for his “offensive words” following the deaths of Colin Powell, the former secretary of state, and Senator John McCain. “That’s who Donald Trump is,” he said.

He also pointed to the examples of Florida and Texas, where Republican leaders have shifted right, and urged Virginians to avoid a similar fate. “The Republican party nationally is for nothing. Not a joke. Nothing.”

But Biden’s sinking approval rating in recent weeks makes it unclear how much of a boost he can offer McAuliffe, who also enlisted Barack Obama last weekend to help him fight apathy and election weariness among Democratic voters. A loss by McAuliffe on 2 November would cause deep anxiety among Democrats and spell trouble for Biden’s presidency.

In the final days of the campaign, both candidates are focused on turning out their base supporters, with Republicans pressing culture war issues, prompting a debate over banning books in high school classrooms.

On Monday the Youngkin campaign released an ad featuring a mother who once sought to have the novel Beloved by Toni Morrison banned from classrooms. The mother’s advocacy led to state legislation, vetoed by Governor McAuliffe in 2016 and 2017, that would have let parents opt out of their children studying classroom materials with sexually explicit content.

Democrats attacked Youngkin’s ad and accused him of trying to “silence” Black authors. McAuliffe’s campaign highlighted the controversy during his rally by passing out copies of Beloved to reporters.

Biden said: “He’s gone from banning a woman’s right to choose to banning books written by a Pulitzer prize and Nobel prize-winning author, Toni Morrison.”

McAuliffe said that Youngkin “is ending his campaign the way he started it: with divisive dog whistles”. He added: “He wants to bring his personal culture wars into our classrooms. Folks, we will not allow Glenn Youngkin to bring his hate, his chaos, into our Virginia schools.”