NEW YORK (NYTIMES) - President Donald Trump and Joe Biden clashed on Wednesday (Sept 2) in duelling remarks and with new advertisements about public safety and the outbursts of violence in some American cities, as the presidential campaign entered an aggressive new phase with the parties tussling over both the issues and the electoral map they are being fought on.

The collisions came as a wave of new polling gave the first significant snapshot of the race since the Democratic and Republican conventions last month.

The polls showed that Biden still holds a steady if not overwhelming lead, tight enough to give Democrats cause for concern and Republicans room for hope, particularly in the key battleground of Pennsylvania.

Polls by Fox News on Wednesday showed Biden leading in Arizona, North Carolina and Wisconsin, all states Trump won in 2016.

While the president has a dwindling number of days to reset a race in which he has consistently trailed this year, Democrats are still wrestling with the asymmetrical nature of battling a candidate willing to make outlandish and false statements in pursuit of victory.

"Get off Twitter," Biden scolded Trump in a speech on Wednesday, urging him to engage with congressional leaders to help support schools and pass an economic aid package.

The former vice president also announced that he would travel Thursday to Kenosha, Wisconsin, where the police shooting of a Black man, Jacob Blake, set off protests that turned violent in places, prompting Trump to tour burned-down areas Tuesday.

Biden will meet with the father and other family members of Blake and hold a community meeting "to heal and address the challenges we face," according to the campaign.

The trip will be only the second one by Biden outside the Eastern time zone since the pandemic locked down much of the country almost six months ago, and comes as some Democratic allies are pressing him to resume campaigning aggressively in person in battleground states.

Biden's top aides, led by his campaign manager, Jennifer O'Malley Dillon, have tried to brace nervous supporters for months that polls would most likely tighten as the election nears.

The new television advertisements were one of the clearest signs yet that the Biden campaign is determined to keep Trump from reframing the campaign as one of fear over the unrest in some cities.

Biden is directing $45 million (S$61.1 million) of the record-breaking $364.5 million he raised in August into a single week of television and digital ads.

While Biden has previously condemned the violence that has accompanied some of the protests for racial justice, his new commercial is the first time that he has put the issues of crime and public safety into a major paid advertising programme.

The ad uses footage from a speech he delivered in Pittsburgh on Monday on the same topic.

"Rioting is not protesting. Looting is not protesting," Biden says in his ad.

"And those who do it should be prosecuted."

The Trump campaign countered with ads featuring images of burning buildings.

"Communities not criminals," says the narrator in the Trump ads.

"Jobs not mobs."

The themes of the ads represent a departure for Biden.

Since he first went on the airwaves in June, nearly 75 per cent of his campaign's television ads have focused on the coronavirus, according to an analysis by the media tracking firm Advertising Analytics.

Conversely, only 5 per cent of Trump's ads have focused on the virus, compared with more than 60 per cent that highlighted the issue of crime.

The political manoeuvres show how both candidates are playing offence and defence at once.

Biden is trying to press his financial advantage and keep the focus on the virus and issues like school re-openings, while also defending himself from Trump's law-and-order attacks.

Trump is trying to prosecute those arguments and persuade voters to see threats to public safety, which so far have been limited to sporadic violence in some cities, while also seeking to gain momentum.

The Biden campaign in recent weeks has pressed particularly aggressively into Florida, airing nearly $15 million in advertising in the last three weeks of August, more than it had spent in the preceding eight weeks combined.

"Biden is in a better place in Florida today than we were in 2008 or 2012," said Steve Schale, who was a top Florida strategist for Barack Obama's two races in the state and now runs a pro-Biden super PAC.

Obama carried the state both times.

The Trump campaign has made a major push in Minnesota, which he lost narrowly in 2016, and the Biden campaign recently began advertising in the state a week earlier than expected.

One of the new Trump ads was crafted specifically for Minnesota, where the police killing of George Floyd first set off the ongoing reckoning over race and police violence and where some protests first turned into looting and rioting.

For the second time this week on a call with reporters, Trump aides maintained that Biden had not sufficiently denounced the violent episodes that grew from the unrest because he hadn't specifically named Antifa, a loose group of activists that Trump's team has tried to paint as a unified, well-financed effort.

"This is exactly the kind of decision-making that we would see emanating from the White House," said Tim Murtaugh, a Trump campaign spokesman, calling the large ad buy an effort to "dissuade" Americans that Biden isn't a "tool of the radical left."

Stephanie Cutter, a Democratic strategist who oversaw messaging and planning for last month's convention, said her party needed to relentlessly focus on the fact that such scenes are playing out under Trump's tenure.

"Anytime Trump wants to talk about the state of this country, it's important to remind people that Trump is president and is responsible for the state of the country," she said.

To the frustration of some in the Biden campaign, it has been fielding concerns and complaints about how the issue of law and order will play in the final nine weeks.

Biden's press secretary, TJ Ducklo, posted a link on Twitter to a new Quinnipiac poll on Wednesday that showed Biden with a 10-percentage-point lead nationally and with an advantage over Trump on the question of who would make respondents feel safer as president.

"cc: bedwetters," Ducklo wrote, in a dig at nervous Democrats.

In North Carolina on Wednesday, Trump appeared to encourage voter fraud, suggesting that people vote twice in order to test the system's ability to detect when more than one ballot is cast.

It is illegal to vote more than once in an election, and Trump has spent weeks trying to cast doubt on mail-in voting.

Democratic Representative Chrissy Houlahan, who was first elected in the 2018 midterms, said it was critical for Democrats keep the focus on the fact that Trump is president now.

"You see the scary images," she said of violence in Oregon and Wisconsin.

"Those are the images we're living in right now and this is the administration responsible."

Houlahan described herself as "cautiously optimistic" about the state of the race in her home state.

"But," she added, "I also felt optimistic four years ago."